Objective: To study the effect of storage temperature on the concentration of the active principles of pesticides phoxim and deltamethrin collected from the Egyptian market. Two packages of phoxim and deltamethrin were analyzed for the active ingredients by using validated HPLC methods with a limit of detection= 0.82 microgram per milliliter and 0.27 microgram per milliliter and limit of quantification= 2.47 micrograms per milliliter and 0.83 microgram per milliliter for phoxim and deltamethrin respectively which indicates its sutability for stability investigation of insecticides, after 21 days of storage at 54 °C and 3 months at room temperature and tested for acute toxicity in albino rats at the beginning and the end of the experiment (3 months). Storage of pesticides decreases their concentrations. The initial concentration of phoxim(500 mg/ml) decreased to 403,364 and 311 mg /ml while that of deltamethrin (50 mg/ml) decreased to 38.8, 35.5, and 29.5 mg/ml after 1 week,2 weeks, and 3 weeks respectively after storage at 54 oc while phoxim concentrations decreased to 460,410, and 395 mg/ml and deltamethrin to 40.3, 36.4, and 31.15 mg/ml after 1, 2, and 3 months at room temperature respectively.. Concerning LD50, phoxim LD50 at the beginning of the experiment was 1660 mg/kg.b.wt and decreased to 831.7 mg/kg.b.wt while deltamethrin LD50 was 17.37 mg/kg.b.wt at the beginning of the research and increased to 20.89.mg/ kg.b.wt.In conclusion: Phoxim and deltamethrin pesticides are degraded by temperature. We should apply the optimum storage conditions and analysis of the marketable pesticides.