The process of electrodeposition of beta-PbO thin films from aqueous solutions of Pb-II salts has been studied in detail. Contrary to the mechanism assumed in previous studies, thin films of crystalline beta-PbO are obtained after cathodic electrolysis in aqueous solutions of various soluble salts of Pb-II (Pb(NO3)(2), Pb(ClO4)(2), and Pb(CH3COO)(2)), and in both the presence and the absence of O-2, thus indicating no contribution of OH- generation by electroreduction of NO3- and/or O-2 to the formation of beta-PbO. A gradual color change is noted: a freshly electrodeposited gray film turns yellow as it dries in air. Drying of the films under controlled atmosphere (Ar or O-2), combined with scanning electron microscopy (SEM) observation and X-ray diffraction (XRD) measurement, has revealed that freshly deposited films are of metallic Pb, which are oxidized and converted into beta-PbO. Such a reaction is operative only when a freshly electrodeposited activated wet Pb film is in contact with gaseous O-2. Despite the rapid conversion of a solid material, the resultant beta-PbO thin films are highly crystallized and possess highly ordered internal nanostructure. Elongated nanoparticles (30 nm x 100 nm) are assembled in a regular alignment to compose a large platelet (greater than 1.0 mum in size) with single-crystalline character, as revealed by transmission electron microscopy (TEM) observation and selected-area electron diffraction (SAED) measurement.