One man grabbed and pulled her hair from behind.
The 21-year-old had left the Bridge nightclub in the early hours of May 10th, when she was surrounded by the group.
Police say the men were speaking in a 'foreign language'.
One of them touched her inappropriately and shouted a foreign word, before the group ran away.
It happened as the victim was walking up George Street to Magdalen Street, between 2.30 and 3.30am.
The offenders have been described at being tanned, Eastern European, and aged in their late twenties.
They were 5ft 8ins to 5ft 11ins tall, all had dark hair and medium builds. One of the men was wearing a brown leather jacket which was not zipped up.
Investigating officer Sergeant Christopher Ball, based at Cowley police station, said: "I would like to speak to anyone who saw what happened or has any information which could assist our investigation.
"The victim is being supported by officers, following the distressing incident.
"If you have any information about this sexual assault, please contact police."
Anyone with any information should contact the 24-hour Thames Valley Police enquiry centre on 101 quoting the reference 43190140470.