More than 800,000 people have viewed the video entitled ‘Philadelphia Police Brutality’, which was posted on a popular video sharing site.
The incident occurred in Philadelphia after a parade on Sunday when officers stopped a motorist during a neighbourhood celebration.
Some people in the crowd apparently threw some liquid on the police officers, and an officer confronted the victim who may have been involved.
The uniformed cop was seen on the tape hitting the woman in the face, and moments later, the woman's mouth appeared to be bloody.
(With inputs from NDTV)