So far police have not had any leads, despite releasing a photo of the suspect - who was caught on camera shopping after the robbery.
He was wearing a baseball cap and a polo shirt belonging to the Austrian Post, which he had taken from the driver of the van.
He left the driver handcuffed in the vehicle after taking the cash in the Wehlistraße, in the district of Brigittenau.
The unarmed post office employee had been travelling alone, collecting money from supermarket branches and was about to take it back to the Austrian Post headquarters.
Police assume that the suspect must have had some inside information as to the driver’s movements. He had a gun and escaped on foot after taking the money.
Police are asking anyone with information to call 01 31310, extension 33800. The post office is offering a reward of €2,500 if the suspect is found.