A total of 257,913 full and part-time students were at college in 2011-12, down 121,320 from 2007-08, figures from the Scottish Funding Council show.
Over the five-year period, the number of people studying full-time at college rose by 19%, to stand at 81,373 last year.
The Scottish Government highlighted the record number of 16 to 24-year-olds on a full-time, funded college course in 2011-12, at 61,304.
But opposition politicians blasted the SNP administration for the overall fall in student numbers
The Scottish Government is "trying to hide the shameful reality of 121,000 fewer students in our colleges compared to when the SNP came to power", Labour education spokesman Hugh Henry said.
There have been "massive cuts in the numbers of part-time students which is hitting hardest in our poorest communities", he said.
"The SNP has axed part-time courses and SNP MSPs insult those students by calling them 'hobby courses'. The result is 100,000 fewer Scottish women are in college now than when the SNP came to power.
"The SNP are no friends of our colleges. Scotland's colleges remain the poor cousin, often overlooked and all too often neglected. Colleges, students and staff won't let Mike Russell spin his way out of the mess he's created."
Tory education spokeswoman Liz Smith said: "Since the SNP came to power in 2007, total student numbers in our colleges have fallen by more than 120,000 and colleges have been so badly affected by successive savage spending cuts."
It is "deeply concerning" that colleges had almost 50,000 fewer students last year than in 2010-11.
"Some of that fall has been as a result of greater focus on the provision of full-time vocational courses for which the completion rates are, encouragingly, very much better. However, this is no consolation to the thousands of part-time students who are struggling to get a college place," she said.
"At a time when employers are asking colleges to provide more courses which reflect the diverse needs of the working population, the decline in overall student numbers is a major concern."
The Scottish Government commitment to maintain student numbers so colleges have the equivalent of 116,000 full-time students has been met, with the equivalent of 119,448 full-time learners in 2011-12, the figures show.
Meanwhile more students are achieving their qualifications at college. In 2011-12 almost two-thirds of full-timers (64%) studying towards a recognised qualification successfully completed their course, up from three-fifths (60%) in 2009-10.
Around two-thirds (65%) of students from the most deprived areas successfully completed their course.
Education Secretary Mike Russell hailed the figures as "excellent news" for colleges.
"Not only are our student numbers targets being exceeded but more young people than ever before are benefiting from full-time courses and more are successfully completing their studies. This is especially true for young people from more disadvantaged backgrounds," he said.
The Scottish Government's commitment to the further education sector is "clear", Mr Russell insisted.
"We have increased funding by £61 million over the spending review period, compared to plans in the draft Budget statement and we are giving the sector the necessary framework for better college governance through the Post 16 Education Bill.
"Today's figures show we are creating an improved college system from a position of real strength."
John Henderson, chief executive of sector representatives Colleges Scotland, said colleges "continue to deliver improvements in the outcomes for learners".
He said: "Completion rates are up again this year for both further and higher education students in almost every category."
Four in every five students aged 16-24 are completing their course of study. Around three-quarters of students from the poorest backgrounds (77%) and four-fifths of those with disabilities are gaining credits and qualifications (80%), Mr Henderson said.
"A high proportion of people studying in colleges start with no qualifications at all and achieving this level of success is a significant and life-changing achievement for those individuals. Colleges are committed to maintaining these achievements and successfully delivering the reforms now under way."
Mr Russell responded to opposition attacks on college numbers, saying: "Headcount and enrolment are measures of limited value when looking at college activity. They do not distinguish between short, part-time courses and those that are longer and more intensive.
"The same economic value cannot be attached to both, which is why the full-time equivalent figure is the one which has been consistently used and the only one from which meaningful comparisons should be made.
"Colleges are delivering more meaningful provision to young people and are improving outcomes such as successful completion and retention. In delivering on full-time equivalent student numbers, colleges are exceeding our commitment and ensuring thousands of young people have the best possible chance of finding a job."
Liberal Democrat education spokesman Liam McArthur said: "SNP ministers shouldn't get their party poppers out just yet. The Education Secretary has flat-out denied that his college cuts have had any negative impact on opportunities.
"This report lays out in black and white the grim fact that there are 121,320 fewer opportunities for potential college students than when the SNP came to power.
"That is a real problem for people who want to study part-time, perhaps to juggle family responsibilities or hold down a temporary job at the same time. If we want to tackle unemployment across the board, everyone deserves a fair crack of the whip regardless of background or family commitments."
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