A seed-borne, aphid-transmitted virus was found infecting mungbean (Vigna radiata) in various regions of Thailand. The pathogen was seed-borne in mungbean and bean (Phaseolus vulgaris). The plants showing systemic symptoms by mechanical inoculation of the virus were limited to the Leguminosae. Infectivity of crude sap of leaves was lost by heating at 50-60°C for 10 minutes, by diluting to 10^-3-10^-4, and by aging at room temperature for 4-8 days. The virus consisted of flexuous filaments about 750 nm in length and was transmitted by aphids in a non-persistent manner. In double-diffusion tests in agar gel plates containing 0.5% lithium 3,5- diiodosalicylate, the virus reacted strongly with antisera to bean common mosaic virus (BCMV) isolated from bean, blackeye cowpea mosaic virus, and azuki bean mosaic virus. Based on host range studies, symptoms, seed and vector transmission, serology, and particle morphology, the virus was identified as a strain of BCMV.