Jayaraman Kannan, a bio-technologist, yesterday pleaded guilty to using criminal force to outrage the 19-year-old girl's modesty on a Singapore Mass Rapid Transit (MRT) train in August last year.
The defendant could have been jailed for up to two years, or fined, or both.
Jayaraman rubbed his crotch against the victim's buttocks and when she turned around he zipped up while travelling on the train between Choa Chu Kang and Bukit Batok stations, the Straits Times reported.
The girl reportedly slapped him and informed the train staff. Police arrested Jayaraman soon after the incident.