Thin molybdenum disilicide (MoSi2) films have been produced by magnetron sputter deposition, and subjected to oxidation tests for the study of "MOSi2 pest" - a phenomenon showing disintegration of a solid piece of MoSi2 into powdery products. The as-prepared films were of an amorphous structure. Oxidation of the films in air at 500-degrees-C led first to cracking of the films, and then the cracked pieces eventually evolved into disintegrated powders with a yellowish appearance. Secondary electron microscopy and Auger electron spectroscopy revealed that the reaction products consisted of MoO3 whiskers (platelets), Si-Mo-O fibres, SiO2 clusters, and some residual MOSi2. The disintegration of MOSi2 films appeared to be independent of their crystal structure; a similar phenomenon was also observed in crystallized films, with a metastable hexagonal structure, oxidized under the same conditions. The disintegration of the MoSi2 films is compared to and correlated with the "pest reaction" of bulk MoSi2.