A series of twenty substituted 3,4-dihydropyrimidine derivatives were prepared and characterized by TLC, IR, ¹H NMR, ¹³C NMR spectroscopic data and elemental analysis. These were screened for insecticidal activity by the film residue method against the pulse beetle (adzuki bean weevil, Callosobruchus chinensis). 4-(2′-Chlorophenyl)-6-phenyl-3,4-dihydropyrimidine-2(1H)-thione (LC₅₀ 0.00201 mg/cm²), 4-(2′-chlorophenyl)-6-p-tolyl-3,4-dihydropyrimidine-2(1H)-thione (LC₅₀ 0.00122 mg/cm²), 4-(4′-methoxyphenyl)-6-(4″-methylphenyl)l-3,4-dihydropyrimidine-2(1H)-thione (LC₅₀ 0.00164 mg/cm²), 4-(4′-chlorophenyl)-6-(4″-methoxyphenyl)-3,4-dihydropyrimidine-2(1H)-thione (LC₅₀ 0.00175 mg/cm²) were found to be more effective than dichlorvos (2,2-dichlorovinyl dimethyl phosphate, LC₅₀ 0.00243 mg/cm²), a commercial insecticide recommended for managing Callosobruchus chinensis.