An efficient vapor-activated power generator based on a 3D polypyrrole (PPy) framework was demonstrated for the first time. By constructing the anions gradient in the PPy, this specially designed PPy framework provided free ionic gradient with the assistant of absorbing water vapor to promote the spontaneous transport of ionic charge carriers, thus leading to the intermittent electric output with the change of external water vapor. A high voltage output of approximate to 60 mV and power density output of approximate to 6.9 mW m(-2) were achieved under the moisture environment. More interestingly, it also exhibited power generation behaviors upon exposure to most of organic or inorganic vapors, indicating the potential new type of self-powered vapor sensors for practical applications.