[Objectives]  To clarify the inheritance of resistance to avermectin+pyridaben in Tetranychus truncatus Ehara. [Methods]  Resistant (RR)and susceptible (SS) strains of Tetranychus truncatus Ehara were crossed and backcrossed to investigate the genes involved in resistance to avermectin+pyridaben, their dominance (D) and cytoplasmic factors involved in resistance. [Results]  D values for F₁ females from SS♀´RR♂ crosses and RR♀´SS♂ crosses were in the range of 0 < D < 1 (0.625 and 0.802, respectively), indicating incomplete dominance. The 95% confidence limits of these two D values overlap, indicating that there is no significant difference between D_SR and D_RS. This reveals that the gene responsible for resistance is located in the autosome. A Chi-square (χ²) goodness-of-fit analysis indicated that mortality levels in F₂ females (BC_1SR and BC_1RS) were significantly different (χ²= 16.92, df = 9, P < 0.05) from the expected values for multiple gene control. [Conclusion]  The inheritance of resistance to abamectin+pyridaben in T. truncatus can easily cause a wide spectrum of resistance that is difficult to reduce. Consequently, abamectin+pyridaben should be used in rotation with the other insecticides to reduce selection for resistance to this combination of insecticides. It’s important to implement a preventive resistance management strategy and measures to manage resistance to abamectin+pyridaben.