There were 1382 reported cases of life-threatening C.diff last year - around one fifth of the 6430 cases reported in 2007, Health Secretary Alex Neil said.
Government figures show there were 608 cases reported in the first six months of the year - less than half the total reported cases for 2012, Mr Neil revealed in response to a parliamentary question.
The SNP's Bob Doris, deputy convener of Holyrood's Health Committee, said the reduction demonstrates "the dramatic impact the SNP's focus on tackling hospital-acquired infection has had".
He added: "Last year, there were over 5000 fewer people aged 65 or over reported to have C.diff since the SNP came to power.
"That is a fantastic achievement under the SNP and could not have been achieved without the hard work and dedication of our health service.
"There have been falls across every NHS board in Scotland."
He added: "Investment in tackling HAIs, bringing cleaning back into the public sector and establishing the Healthcare Environment Inspectorate are all key steps taken by the SNP to cut C.diff rates across Scotland."