A Maddington man has been assaulted and robbed at gunpoint after picking up a hitch-hiker on Wednesday night.

The 22-year-old man was driving a green Toyota Celica along Tonkin Highway when he picked up a male hitch-hiker near Abernethy Road in Forrestfield.

As they approached Canning Mills Road in Roleystone, the hitch-hiker pulled a gun and assaulted the driver, stealing his wallet and mobile phone. 

Police spokesperson Susan Usher said police believe the hitch-hiker took off on foot.

The hitch-hiker was described as 50 to 60 years old with tanned white skin and brown short-cropped hair.

The driver was treated at Armadale Hospital.

Anyone with information should call Crime Stoppers on 1800 333 000.