The incident happened just after 1 a.m. at a large dance party on the Keele campus.
The woman was not injured in the incident. Police are working on a description of the suspect.
Over the last few years, several sexual assaults have been reported on campus.
In 2011, York increased its security budget by more than $ 1 million dollars and added extra security.
They also added extra security phones and lighting across Keele campus.