Police said a 28-year-old woman was taken to New York Presbyterian Hospital but is expected to survive.
The slashing happened at the Lexington Avenue and East 86th Street 4/5/6 train line just after 6 p.m. on Monday.
Police said the suspect was wearing a black ski mask and fled on foot.
The investigation is ongoing.
* Get Eyewitness News Delivered
* Follow us on YouTube
* More local news
* Send us a news tip
* Download the abc7NY app for breaking news alerts