The incident happened at around 1.30pm on Friday June 14 when a 32-year-old man was delivering parcels at an address in Hall Lane.
A spokesman for the police said the man was grabbed around the neck by a man carrying a knife who then threatened the worker, taking his keys. The attacker then pushed the victim out of the way and stole his van containing more than 100 parcels.
The man drove off towards the A59 Liverpool Road area with the van, a silver Vauxhall Vivaro which was later found empty and abandoned in Smithy Lane, Much Hoole.
The offender is described as male, aged 20 to 30-years-old, around 5ft 7in tall. He was wearing dark clothing and a dark coloured cap.
Police are now appealing for information and are urging anyone who witnessed the incident to contact officers.
Det Con Richard Clancy, of Preston CID, said: “We are appealing for information following a robbery in a residential area in the outskirts Preston.
“Luckily the van driver wasn’t seriously hurt but he has been left extremely shaken by his ordeal.
“We suspect the stolen silver van was in company with another vehicle which has been used for the getaway and may have been in the area some time beforehand.
“I urge anyone with any information at all to come forward.”
Anyone with information about the incident or about the offenders can contact police on 101 quoting log reference 0759 of July 14.
Alternatively, they can contact Crimestoppers anonymously on 0800 555 111 or online at Crimestoppers-uk.org. No personal details are taken, information is not traced or recorded and you will not go to court.