In this paper, the structure, electrical and optical properties and stabilities of Ag doped p-type ZnO thin films, prepared by electrostatic-enhanced ultrasonic spray pyrolysis were investigated. XRD and Hall data analyses indicated that the resistivity of 4at. % Ag doped p-type ZnO was low, without Ag2O phase separation. The optical transmission spectra illustrated that optical band gaps decreases with the gradual increase of Ag dopant. Moreover, ZnO: Ag films placed for 10 days still showed p-type, but the optical transmittance decreased, suggesting that AgZn in the ZnO: Ag thin films captured electrons to generate Agi, which reunited to be Ag nano-particles and decreased the optical transmittance of ZnO: Ag.