Hazelnut, as with many other stored products, are susceptible to infestation by a variety of stored insect pests. Phosphine fumigation is a widely used method to control pests in stored products, including hazelnut kernels. This study aimed to determine the optimal exposure time for phosphine fumigation for management of stored product pests in hazelnuts. Four treatments with different exposure times (3, 4, 5, and 6 days) were conducted using various development stages of Oryzaephilus surinamensis (L.) (Coleoptera: Silvanidae), Tribolium confusum Jaqcquelin du Val, (Coleoptera: Tenebrionidae), Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae), Ephestia kuehniella Zeller (Lepidoptera: Pyralidae), and Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae) together with the control group. The trials were conducted in a commercial chamber of a hazelnut processing facility. The insects were placed in plastic containers within jute sacks filled with hazelnuts, fumigations were done under gas-proof sheet and the survival rate was assessed after treatments. The results showed that a 3-day exposure period was sufficient to fully eradicate the pupal and adult stages of O. surinamensis. For T. castaneum, 100% mortality was achieved in both larvae and adults from 3 days of exposure, but the pupal stage required at least 5 days. For T. confusum, all larvae and adults died in all exposure periods, but the pupal stage required at least 4 days. In the case of the moth species, a 100% mortality rate was achieved in the larval and pupal stages of both E. kuehniella and P. interpunctella at all exposure periods. The mortality rate of E. kuehniella eggs was 99% after 3 and 4 days of exposure, and a fumigation period of 5 days was required to control the entire population. However, only 67% of P. interpunctella eggs were controlled after 3 days of exposure. The time and stage factors were found to be significant in the egg stage of P. interpunctella. The results suggest that a 5-day exposure period is the most effective for controlling tested stored product pests in hazelnuts.