A 72-year-old woman in a wheelchair was attacked at Blacktown station on Wednesday about 5.45pm.
She told police her assailant spun her wheelchair around and indecently assaulted her.
She wheeled herself to the station's barriers and reported the incident.
She described the man as being of Indian or subcontinental appearance and about 30 years old. He was of medium build and had short black hair.
The man was wearing a grey jumper, dark jeans and dark shoes.
Police urge anyone with information to contact Blacktown detectives on 9671 9199 or Crime Stoppers.