The rice leaf bug, Trigonotylus caelestialium (Kirkaldy), is an important species of stink bugs causing pecky rice. Control of this bug with fenitrothion is insufficient in paddy fields of Niigata Prefecture. Therefore, susceptibility to fenitrothion was assayed in populations sampled from seven regions of Niigata Prefecture in 2001 and 2002. LD₅₀ values of five populations ranged from 50.6 to 146.2 μg/g, and these values were remarkably higher than 18.8 μg/g of the most susceptible population tested. I concluded that resistance to fenitrothion developed with continuous applications of fenitrothion.