Mycobacterium avium complex (MAC) infection has been giving major impact on human health. MAC infection is also one of zoonosis transmittable from environmental reservoirs to domestic animal such as pig, and from wildlife to human. Although the relationship between pig MAC infection and human MAC infection has been suggested, it has not been clarified about difference of pathogens, differences in the pathogenesis of the disease, and differences in pathological findings between them. As one of zoonosis, hog farms suffer from the epidemic in pig population and it may causes huge economical loss. At the same time, from pig to human transmission of MAC has been worried. Therefore, the control of MAC infection among hog farms is a very important issue both for pig industries and for human public health. We have demonstrated that the specific MAC strains can spread through pig market in the main island of Okinawa. In pig MAC infection, pathogens are infected orally, and granulomatous lesions are formed in abdominal lymph nodes. Subsequently, it spreads lymphogenously or hematogenously and forms disseminated disease. Pathologically, calcified lesion was formed within several months. These findings are quite different from human MAC disease, in which the infection was caused by inhalation, and form granulomatous lesions in lungs, and rarely cause lymph node swellings. Since the pathogenesis of human MAC respiratory infection has not been well clarified, it may be very important to examine the mechanism of pig MAC infection to find out some clues to explain the mechanism of human MAC infection.