PROBLEM TO BE SOLVED: To provide a method for treating a used paper diaper by which the diaper can be disinfected and treated without requiring a large amount of water.SOLUTION: The method for treating a used paper diaper includes: introducing lime 1, 1,000 ppm or 1,500 ppm of a hypochlorite 2, and the used paper diaper 4 into a treating vessel 3； performing stirring for a prescribed time using water which has been absorbed in the used paper diaper 4 decomposed by the lime 1 while feeding water 5 in a minimum amount capable of being stirred into the treating vessel 3； discharging a liquid 6 in the treating vessel 3 to the exterior of the treating vessel 3 and dehydrating the treated product； collecting and subjecting waste water 7 discharged from the treating vessel 3 to water quality treatment； and discarding the treated waste water.
