Propoxur, a carbamate insecticide, has been used worldwide for the control of house flies (Musca domestica L.) for many decades. Resistance levels to propoxur have been detected in field populations of house flies in many parts of the world, including China. In this study, a near-isogenic house fly line (N-PRR) resistant to propoxur was used to determine the mode of inheritance. Bioassay results showed no significant differences in LD₅₀ values or in the slope of log dose-probit lines between the reciprocal F₁ and F₁′ progenies, and the degree of dominance (D) was more than −1 and less than 0. Chi-square analysis of the responses of self-bred (F₂, F₂′) and backcross progenies (BC₁, BC₂, BC₁′, and BC₂′) indicated that a single gene was responsible for resistance. Propoxur resistance in the N-PRR strain of house fly was inherited as a single, major, autosomal, and incompletely recessive factor. These results should be useful to reveal the mode of inheritance and the development trend of propoxur resistance and develop a systematic strategy for the resistance management in house flies.