There is disclosed a method for measuring the strength of a honeycomb structure provided with an insertion hole preferably without generating any chipping. In the strength measuring method of the honeycomb structure, the strength is measured while a rubber plug is inserted into the insertion hole. The rubber plug has a hardness of 45 or more and 90 or less, a clearance between the inserted rubber plug and the inner surface of the insertion hole parallel to the depth direction of the insertion hole is 0.2 mm or more and 2.6 mm or less, and the protruding height of the inserted rubber plug from the peripheral surface of the honeycomb structure is 0.5 mm or more and 5 mm or less.