Sometime between 5.30pm on Friday 10 June and 8am on Monday 13 June 2011, offenders broke into Kirby and Co Financial Advisors, on the High Street, in Starbeck.
They gained entry to the premises by forcing a side window and once inside stole £248 worth of first and second class stamps.
Officers investigating the burglary are appealing for anyone with any information to come forward.
PC Ross Hakin, of Harrogate police, said: “This is a rather unusual theft and one we are keen to get to the bottom of.
“Anyone offering to sell a large number of stamps will stand out quite clearly and I am appealing for the public to keep their eye out for anyone trying to offload a large quantity of them.
“I am also appealing to anyone who saw any suspicious activity on the High Street, in Starbeck, over the weekend to contact the police or Crimestoppers with information.”
Anyone who can help the police with their enquiries is urged to contact PC Ross Hakin, of Harrogate police, on 0845 60 60 24 7, quoting reference number, 12110096857.
Alternatively, Crimestoppers can be contacted anonymously on 0800 555 111.