Scottish Court Service (SCS) data reveals that between July 2011 and June 2012, the total of fiscal fines, justice of the peace court fines and police fixed penalties for anti-social behaviour was £14 million, 31% of which was in arrears.
In 2009-10, £12.4m of sheriff court fines were issued, 10.7% of which was in arrears.
The figures have raised question marks over Scottish Government plans to force criminals to pay into a fund to help compensate victims of crime. The Government estimated more than £1.2m a year could be raised.
Lewis Macdonald, Scottish Labour's justice spokesman said: "The revelation that thousands of discharged fiscal direct penalties are simply abandoned will come as a shock to the Scottish public."
A Scottish Government spokesman said: "Fine collection is a matter for the SCS and it is working hard to enforce fines.
"Since it took over responsibility, collection rates have improved and are now at their highest ever recorded level."