Since 1954 the authors have tested the control effect on soil treatment of insecticides against the main insect pests of rice plants. The insecticides tested for this purpose were parathion, methyl-parathion, Dipterex, lindane, Sevin, Metasystox, Disyston, Thimet and others. Among them lindane and Sevin (wettable) are the most effective against insects and the best suited for soil treatment.In 1959 the control effect of soil co-treatment with crude lindane and Sevin wettable 50% against the main insect pests of rice plants was tested in pots and in field. The result of the experiment is as follows :1. The every treated plot controlled exceedingly well the occurrence of rice stem borers, green rice leafhoppers, brown planthoppers and the other planthoppers, both in pots and in fields.2. Regarding the yield the ratio of the treated plot to the untreated plot was 140.78-171.84: 100, in weight of brown rice. This indicates an increase of 41-72%.3. The control effect of single treatment (at transplanting time) lasted at least for two months, however, it did not retain its effectiveness untill harvesting time, even in the most heavily treated, i. e., crude lindane 1kg/10a and Sevin wettable 50% 4 kg/10a.On the contrary, double treatments (the first at transplanting time and the second on the 20th of August, or five days before the peak of the second moth appearance of the rice stem borer) controlled main insect pests untill harvesting time. The minimum dose for control in each case was crude lindane 0.5 Kg/10a and Sevin wettable 1.5 kg/10a.