Transmission tests of rice ragged stunt virus in Thailand were conducted. Nilaparvata lugens transmitted the disease in a persistent manner and the incubation period in the insect ranged from 4 to 17 days with an average of 8 days. The minimum acquisition access period was 3 hr and the minimum inoculation access period was 1 hr. The 5th and 4th instar nymphs of N. lugens showed higher transmission efficiency than other instar nymphs and adults. Nilaparvata bakeri transmitted the ragged stunt virus but Nephotettix virescens, Recilia dorsalis, and Spgatella furcifera did not. Dual infection of ragged stunt and grassy stunt viruses in rice plant occurred by inoculation through N. lugens which dually acquired the viruses, suggesting the absence of cross protection between ragged stunt virus and grassy stunt virus. Spherical particles about 60 nm in diameter were observed in the dip preparations from the diseased leaves.