Filter cake and Triplex are powdered by-products of aluminum sulfate and soap factories in Ethiopia, respectively. This study was aimed at determining contact toxicity of filter cake and Triplex powders against maize weevil, Sitophilus zeamais Motschulsky. Lethal concentrations for 99% mortality (LC₉₉) against S. zeamais were determined by exposing adults for 12 h to filter cake (0.5–8 g/m²) and Triplex (1–9 g/m²) in concrete arenas. Lethal times for 99% mortality (LT₉₉) were determined by exposing adults over time (1–24 h) in concrete arenas to 3 g/m² of filter cake and 9 g/m² of Triplex. Exposed adults were transferred to containers with 30 g of organic wheat and held at 28°C and 65% RH for 14 d to determine mortality. LC₉₉ values for S. zeamais adults were 7.54 and 23.46 g/m² when exposed to filter cake and Triplex, respectively. The corresponding LT₉₉ values were 21.92 and 39.62 h when exposed to filter cake and Triplex, respectively. Effective concentrations and times for the 99% reduction of progeny production were determined from percentage reduction in adult progeny relative to production in control treatments after 42 d. EC₉₉ values for progeny reduction were 2.48 and 18.59 g/m² for filter cake and Triplex treatments, respectively. The corresponding ET₉₉ values for progeny reduction were 17.49 and 22.31 h for filter cake and Triplex, respectively. Sitophilus zeamais exposed to filter cake produced lower percentage insect-damaged kernels and weight loss thanTriplex. Filter cake was more efficacious against S. zeamais than Triplex.