A laboratory studies were undertaken to assess the efficacy of Diazinon insecticide (EC). Formulation of insecticide were applied to different surfaces i.e. steel, ceramic, wood and cement at 0.0006 and 0.0003 ml / cm2 to determine their persistence up to 28 weeks against Sitophilus oryzae (L.) and Rhizopertha dominica (F.). Insects were exposed on the treated surfaces for 24 hrs. at 28 weeks after treatment. Results indicated that; mortality rates were positively corrected with the concentration and negatively corrected with the time of application. The results indicated that:  Steel and ceramic were the most persistent surfaces which gave 100 % mortality up to 18 and 20 weeks at the highest concentration in both tested insects respectively.  Wood surface can provide good protection only up to the tenth and eighth weeks after application at the highest concentration for S. oryzae and R. domonica respectively.  In cement surface, Diazinon deteriorated very rapidly starting from the first two weeks at 0.0006 ml / cm2 on both tested insectsValues of gross persistency of the different surfaces indicated that steel and ceramic surfaces were the most ideal to retain toxicity followed by wood surface, meanwhile cement surface lost most of its efficiency when used.  Finally, Rizopertha dominica (F.) adults were more tolerant to insecticide than S. oryzae (L.)