Robert Roberts, 60, formerly of Hathersage Way, Sutton in Ashfield, has been sentenced to four years and four months in prison.
He had previously pleaded guilty to eight counts of sexual activity with a person with a mental disorder.
Roberts used his position at a mental health centre in Nottinghamshire to befriend the woman when he began working there in 2013 and the activity only stopped when the victim reported the incidents in late 2014.
Detective Inspector, Nikki Smith, said: “We are pleased with the outcome of this case. Roberts abused his position of trust, targeting a vulnerable patient while working at a mental health unit. This sentence sends out a strong message that we will investigate serious offences of this nature and get justice for victims.”