The study investigated the role of Catholic missionaries in the development of health services in Kihanja and Ihangiro chiefdoms in Bukoba District from 1904 to 1961. The specific objectives of the study were to describe evolution of Catholic missionary health services in relation with the colonial states’ medical policies; to identify curative and preventive roles of Catholic missionaries in the development of health services, and to explore the role of missionary health services in transforming Africans from traditional to Western medical treatment in Kihanja and Ihangiro chiefdoms. The researcher employed historical design and qualitative approach where documentary, in-depth interviews and observation methods were used to collect data. The research reveals that colonial governments’ health services concentrated in urban areas while medical missions provided both curative and preventive health services mainly in rural areas. Moreover, the study demonstrates that though many Bahaya people in Kihanja and Ihangiro were converted to Christianity and eventually introduced to Western medical practice, they did not totally shun away from their traditional healing systems. The practice of both healing systems co-existed depending on the nature of the disease and the system that assured them effective relief. It is concluded that medical missions were vital to the development of health services for the sake of African rural population. In addition, missions’ collaboration with the government was not done to perpetuate colonialism but was only accepted where missions’ interest of curing the body and saving African souls was guaranteed, but where it was not, missionaries normally abstained.