The growth of Ag ultramicro-particles in BaO semiconductor film are investigated bv tran missive electron microscope. The fine growth of Ag ultramicro-particles in BaO film are discovered in the samples after proper heat treatment. We also contrasted the structure difference of single-layer-made and multilayer-made Ag + BaO films. The growth properties of Ag ultramicro-particles in Ag + BaO films with different Ag content are also studied. The Ag ultramicro-particles do not form maze structure in Ag + BaO film with high Ag content, but form isolated Ag particles. There are BaO layer of a few nm thick between every two Ag particles.