The large bumblebee, Bombus terrestris, which is indigenous to Europe and is used extensively for high-value crop pollination, has been artificially introduced throughout the world. Here we show the interspecific cross-mating between bumblebee species, B. terrestris and B. ignitus under laboratory conditions. The mating and oviposition rates of interspecific cross-mating of B. terrestris queen with B. ignitus male are higher than those of intraspecific matings of B. ignitus. Furthermore, the competitive copulation experiment indicates that cross-mating of a B. ignitus male with B. terrestris queen is 1.8-fold more frequent than with a B. ignitus queen. The cross-mated B. ignitus queen with B. terrestris male produced B. ignitus workers and B. ignitus male offspring, and the cross-mated B. terrestris queen with B. ignitus male produced both B. terrestris males and B. ignitus male offspring. The genetic tests using a portion of the mitochondrial COI gene for the parent and hybrid offspring indicate that mitochondrial DNA was maternally inherited. Our results indicate that interspecific cross-mating occurred between B. ignitus and B. terrestris, which suggests that the cross-mating is not an exclusive force against the negative impact of competition and genetic contamination on native bumblebees.