The phytotoxic activity of pretilachlor [2-chloro-2′, 6′-diethyl-N-(2-propoxyethyl) acetanilide] on transplanted rice in Utsunomiya and Yawara paddy soils under lowland condition was investigated in relation to its behavior in the soils. The inhibitory activity of pretilachlor on the growth of rice was slightly less when mixed in Utsunomiya soil than in Yawara soil. On the contrary, the growth was inhibited by pretilachlor more remarkably in the former than in the latter when the herbicide was applied into flooded water under water leakage condition. Pretilachlor concentration in soil water was higher in Yawara soil than in Utsunomiya soil by the soil-mix application. With pretilachlor application into flooded water, the herbicide-treated layer was formed in the top layer in Yawara soil but was little formed in Utsunomiya soil. Leaching of pretilachlor was greater in Utsunomiya soil than in Yawara soil, resulting in higher concentration of pretilachlor in soil water in the former. These results suggested that the higher phytotoxic activity of pretilachlor applied into flooded water on the rice transplanted in Utsunomiya soil than in Yawara soil under water leakage condition depended on its higher concentration in the water existing in the soil below the transplantation depth.