A woman ringing in the New Year at Mooseheads was allegedly indecently assaulted on the dance floor, police say.
Police were called to the Civic nightclub shortly after 1am on Friday after the woman was allegedly attacked.
The woman pushed the man off and alerted security, who ejected the man.
Officers took one man to the ACT Watch House but he was later released without charge.
Investigators are now hoping to speak to a woman who reportedly spoke to the victim as security were removing the man from the club.
Canberra's largely subdued New Year's Eve celebrations were marred by arson and underage drinking.
A Queensland man was referred to a mental health facility for examination after he was accused of torching his family's car in central Canberra during the 9pm fireworks while a group of 15 underage drunks was taken into protective custody.
Anyone who may have any information that could assist police in regards to the alleged indecent assault is urged to contact Crime Stoppers on 1800 333 000, or via act.crimestoppers.com.au.
Information can be provided anonymously.