Wide bandgap semiconductor zinc oxide thin films have been prepared by an electrochemical deposition performed in a chemical cell with three-electrodes, using an aqueous solution of Zn(NO_3)_2 as electrodeposition solution. The obtained ZnO thin films have optical bandgap of 3.35 eV and optical transmittance larger than 80% in the range of 400～2000 nm determined from their optical transmission spectra. XRD pattern indicates hexagonal wurtzite structure without c axis orientation for the ZnO thin films. AFM studies show a dense, irregular polycrystalline film structure with grain size below 250 nm. Stimulated emission occurs at a close ultraviolte wavelength of 403.9 nm under 355 nm optical pumping. When the excitation intensity exceeds a threshold (about 196.8 kW/cm2), very narrow emission peak (FWHM=0.5 nm) emerges and its intensity increases superlinearly with increasing the pump power. The stimulated eimission light is multimode laser relative to incident area and can be observed in all directions, showing a random laser emission due to the formation of a closed-loop path for scattered light in the ZnO thin film.