Burglars made off with a safe containing cash after hacking their way through a fire exit at Spalding’s Cancer Research charity shop.
The Hall Place premises were raided overnight on December 23-24.
Police say the safe contained a cash float and some takings.
There was also a raid on a Cancer Research charity shop in Sleaford overnight on December 28-29.
A Lincolnshire Police spokesman said: “At this time of year, people will be remembering loved ones they have lost to cancer and they will be appalled that thieves would target a charity which does so much for those affected by the disease.
“Anyone with information about who may be responsible for these burglaries is asked to contact us.”
• People who know anythng at all about the raids are asked to call police on 101 or Crimestoppers anonymously on 0800 555111.