6ABC Action News in Philadelphia reports that Arthur Robinson, 78, came home after visiting with his grandchildren to find that his home had been burglarized.
Several wooden boxes were swiped from the master bedroom, including one in a green velvet drawstring bag.
That box contained the ashes of Arthur's wife, Nancy, who died of cancer in 2009, Action News reports.
Police said the thieves likely had no clue what they were stealing.
The Robinsons were married for 50 years before she died, and they had three sons and 12 grandchildren.
Police are urging the burglars to return the ashes, "no questions asked," Action News reports. There is also a $1,000 reward.
Get more on this story from our sister station, WPVI-TV.