This contribution sheds new light on the members of missionary congregations who collected natural history specimens and geological samples in the Belgian colony during the first half of the 20th century. The analysis of the Royal Museum of Central Africa s databases and his institutional archives makes it possible to reconstruct the typology of these collectors and to highlight the collection routes and methods used by some of them. They were doubly solicited by the museum as devoted to the cause of scientists and because they offered greater possibilities to rely on the local population. Their dedication to scientific research was a powerful motivating force. Their effective collaboration was then recognized as remarkable even though they were poorly highlighted in the history of the museum and its collections. Current debates about the provenance of the collections are gradually changing this situation. Like other collectors, the contribution of missionaries is now called upon to receive more attention.