Mungbean (Vigna radiata) and rice bean (V. umbellata) (both species 2n = 2x = 22) have desirable traits that complement each other. In this study, we rescued embryos from a cross between mungbean cv. "Kamphaeng Saen 2" and rice bean cv. "Miyazaki" and resolved the hybrid sterility problem by colchicine treatment. The interspecific hybrids were obtained when Kamphaeng Saen 2 was used as the female parent. Four out of 80 immature seeds at 12 days old were able to germinate on an MS medium supplemented with 1 mg $L^{-1}$ IAA, 0.2 mg $L^{-1}$ kinetin, and 500 mg $L^{-1}$ casein hydrolysate. Forty random amplified polymorphic DNA (RAPD) primers were screened for polymorphism among the parents, and two specific primers were finally chosen for testing of hybridity. Using the two primers, all putative $F_1$ hybrids were confirmed as the interspecific hybrids. To observe their fertility, some of the hybrid seedlings were transplanted. The hybrid produced flowers profusely but failed to set pods. To overcome the sterility, plants were induced to become tetraploid by colchicine treatment in vitro. The ploidy level of the regenerated seedlings was confirmed from leaf DNA using a flow cytometer. Three out of 20 hybrid seedlings (15%) were successfully induced from diploid to tetraploid by a colchicine concentration of 2 g $L^{-1}$. The tetraploid hybrids were able to produce flowers and set pods normally.