South Yorkshire Police say a burglar entered a house on Hill Street through the back door between 3pm and 9pm on Friday 18 February.
Between 60 and 70 war medals were stolen, worth around £12,000.
Some of the medals belonged to the victim's grandfather who served in World War One.
Police are appealing for anyone who may have seen the items for sale or who saw anything suspicious in the area at the time.
Anyone who has information is urged to call 101.