Khapra beetle, Trogoderma granarium Everts is a serious pest that affects stored grains and oilseeds. The current work was carried out to investigate the effect of malathion sublethal concentrations (LC₁₀ and LC₄₀) exposed to first and fourth larval instars on biological aspects and population growth of T. granarium. Results indicated that exposure of 1^-st instar to either LC₁₀ or LC₄₀ had a destructive effect and treated larvae failed to complete their larval stage. While 4^-th instar exposed to the same sublethal concentrations completed their life cycle with considerable impacts on biological aspects and life table parameters. Treatments increased the number of instars molting reaching seven or eightinstars. In contrast, larval, pre-adult, and total longevity periods were decreased in treatments compared with control. Concerning life table parameters such as net reproductive rate (R0), intrinsic rates of increase (r), finite rate (λ), fecundity and mean generation time (T) were decreased compared to control.  The current study clarified thatsublethal concentrations of malathion induce strong adverse effects and suppress the population growth of T. granarium. Our results would be useful to assess the overall effects of malathion on T. granarium and can contribute effectively in pest management.