They say the woman, who fell to the ground as two men tried to grab her handbag in the alley between Victoria Street and Regent Street, received slight injuries and was left extremely shocked by the incident.
A Lancashire police spokesman at Greenbank, Blackburn, said the woman was walking along the alley which runs parallel with Derby Road when she spotted two men coming towards her at approximately 1.15am on Saturday.
She said: “As they came alongside her, one of them grabbed the straps of her handbag and tried to drag her bag off her.
“She struggled, and as a result of this, fell to the floor and as she did so the contents of her bag spilled out.
“The offenders grabbed her purse and took some cash and then ran off down the alley towards town.”
Because it was dark, police said the victim did not get a good look at the offenders, but both men are said to have been white.
One was approximately 5ft 8in or 9in tall and the other 5ft 2in or 3in.
Also, one of the men was said to have been wearing a dark hooded top.
She said the police are appealing for any further information and for any witnesses to come forward.
A full police investigation is underway, house to house enquiries have been taking place and CCTV footage is being studied.
The officer said she would also like others to be made aware of the incident, advising anyone thinking of walking home late at night or during the early hours, particularly if unaccompanied, to stick to the main streets, rather than walking down darkened alleys.
Anyone who can assist the police is asked to contact CID directly on 01254 353593, or ring Lancashire police 101 or Crimestoppers on 0800 555 111.
Longridge Sgt Dave Simpson said it was “unusual” for this type of crime to happen in Longridge, saying: “We need to speak to any witnesses or persons who may know the identities of the offenders.”
• Longridge police are also appealing for further information after a burglary at a semi-detached house on Preston Road between July 2 and 3, during which a small quantity of jewellery and a jar containing up to £150 cash was stolen. Call on 01772 209583 or 101.