Transit Crime Investigation Unit detectives arrested a man following a reported sexual assault on a V/Line train in May.
Following a public appeal in June, detectives arrested a 48-year-old man in Dandenong yesterday.
The Traralgon man was interviewed and is expected to be charged on summons with sexual assault and unlawful assault.
The arrest follows an incident on a V/Line train between Pakenham and Warragul railway stations on 10 May.
Police will allege an 18-year-old woman was approached by a man and sexually assaulted.
Detectives would like to thank the media and community for their assistance with the matter.