Steven Watson carried out the attacks on a man in his 40s who was unable to give consent.
The 64-year-old from Dunfermline, Fife, worked for a charity providing care within a residential care home where he repeatedly assaulted his victim repeatedly between December and January this year.
Management at the home became suspicious of his behaviour and called in police.
Watson pleaded guilty to rape last month, but now he has been sentenced at the High Court in Edinburgh, to six years and four months.
He will be on the sex offenders' register indefinitely.
"Steven Watson used his position to prey on an extremely vulnerable man in what was a despicable breach of trust," said Detective Constable Lauren Miller of Fife's Divisional Rape Investigation Unit. "I want to thank staff for their vigilance in reporting concerns to management and police, and for their co-operation with our investigation.
"Police Scotland is committed to safeguarding people from sexual violence and any reports will be taken seriously and thoroughly investigated."