Abstract: Study was carried out to determine the level of resistance in Tribolium castaneum (Hbst.). Strains collected from various localities of the Punjab and exposed to different concentrations of phosphine, viz; 0.01, 0.02, 0.03, 0.04 and 0.05%. Higher concentration (0.05 percent) gave higher mortality (90.721-100 percent) under test. While LC 50 values calculated for Sargodha, Kalar-Kahar, Chiniot, Moza Matu, Noorwala, Okara, Jhang, Mamukanjan, Faisalabad, Lahore and susceptible strains of T. castaneum were 0.0220, 0.0115, 0.0176, 0.0132, 0.0136, 0.0163, 0.2010, 0.0186, 0.0193, 0.0192 and 0.0030, respectively, and the level of resistance in these strains ranged from 3.787 to 7.255.