A woman is in hospital with a fractured spine, broken leg and collapsed lung after she was allegedly run down by her brother in the Blue Mountains yesterday.

The 19-year-old woman was hit by the car on Heather Road at Winmalee about 2:30pm (AEST).

Police say the siblings got into an argument after the woman's cat urinated on her 20-year-old brother's computer.

The man allegedly dragged his sister along the floor then threw the cat against his car before running the woman down outside their home.

The woman was taken to Nepean Hospital where she remains in a serious condition.

Her brother has been charged with common assault and negligent driving.

He has been released on bail to face Penrith Local Court next week.

Police say the cat was not injured in the incident.