A series of experiments were conducted from 1968 to 1970 to find the transmission effects of the dwarf disease of mulberry tree in connection with inlay grafting and insect vector with the following conclusions: 1. The inlay-grafting of sound scions on diseased roots showed a 30 per cent transmission rate among the successful grafts. The inlay-grafting of diseased scions on sound roots showed a 14 per cent transmission rate among the successful grafts ir the case of scions cut and stored before wintering but no transmission effect in the case of scions prepared after wintering, There were some stocks, among the unsuccesful grasfts of diseased scions upon sound roots, that sprouted out new buds, no transmission effects were found in them, 2. Leafhoppers (Hishimonus disciguttus Walker) collected from areas with no dwarf disease infection were grouped into three plots and let to feed on mulberry tree severely infected by dwarf disease for 7 days, 14 days and 21 days respectively. After these preliminary treatment, the leafhoppers were recollected to be fed on the sound seedling divided into three plots for 10 days, 15 days and 20 days respectively to find the transmission effects. The results are that the 7 day plot showed no transmission effect whereas the 14 day plot showed a 22 per cent disease rate and the 21 day plot 61 per cent rate indicating that the longer the feeding period is the higher the transmission rate.