[Aim]  To understand the effects of continuous exposure to S-methoprene on four major stored grain pests. [Methods]  Insecticide-impregnated filter paper was used to measure the larval survival rate, larval mortality rate, pupal survival rate, pupal mortality rate, and emergence rate of four major stored grain pests (Tribolium castaneum, Tribolium confusum, Cryptolestes ferrugineus, and Oryzaephilus surinamensis) after S-methoprene treatment. [Results]  Four weeks of continuous treatment with S-methoprene effectively controlled both C. ferrugineus and O. surinamensis, both of which had a maximum emergence rate of < 10.00%. Most T. castaneum larvae died after 6 weeks of continuous treatment. The T. castaneum emergence rate reached a maximum of 61.67% only at an S-methoprene dosage of 2×10^–5 mg/cm². Only T. confusum had an emergence rate of 41.67% after 7 weeks of continuous treatment at a dosage of 4×10^–5 mg/cm². Compared to the control groups, the larval and pupal stages of all four stored grain pests treated with S-methoprene were prolonged to varying degrees, and this prolongation increased with increasing S-methoprene dosage. [Conclusion]  S-methoprene can control, to some extent, all four major stored grain pests tested, but the degree of control is closely related to the treatment duration and dosage.