A diaper capable of sensing humidity mainly comprises a diaper body to be worn and wrapped on the lower body of a user. When the body fluid such as urine of the user is in contact with a first electrode and a second electrode in the diaper body, different potential difference between the first and second electrodes can be used to activate the body fluid between the two electrodes to generate a power which is then used for driving a warning unit, enabling a caregiver or a nurse to be aware of the replacement timing of the diaper from the warning message issued by the warning unit.
