The large bumblebee Bombus terrestris, indigenous to Europe and adjacent areas and used extensively for high-value crop pollination, has been artificially introduced to several parts of the world. Here we show the occurrence of interspecific hybridization between the bumblebee species B. hypocrita sapporoensis and B. terrestris under laboratory conditions. The mating and oviposition percentages resulting from the interspecific hybridization of a B. terrestris queen with a B. h. sapporoensis male were higher than those resulting from the intraspecific mating of B. h. sapporoensis. Furthermore, a competitive copulation experiment indicated that the mating of B. h. sapporoensis males with B. terrestris queens was 1.2-fold more frequent than the mating of these males with B. h. sapporoensis queens. The interspecific hybridization of a B. terrestris queen with a B. h. sapporoensis male produced either B. terrestris workers or the B. terrestris male phenotype, and the hybridization of a B. h. sapporoensis queen with a B. terrestris male produced B. h. sapporoensis males. Our results indicated that interspecific hybridization occurred between B. h. sapporoensis and B. terrestris. These results suggest that such hybridization will have a negative competitive impact and will cause genetic contamination of native bumblebees.