Organophosphates are the most common pesticides being utilized all over the world. These compounds are toxic which can easily penetrate the water table and other drinking sources during application in crop fields. Since using some drinking water accumulating an amount of toxins of raised value than the standard level, causes unwanted effects on health of human beings. This experiment aimed to investigate the effectiveness of removal of Malathion from water by technique of ultraviolet irradiation (UV) medium pressure and with a Mercury lamp. Methods: In this investigation, variants of initial pH and primary concentrations and exposure times were observed. Initial concentrations of Malathion were 0.5, 1 and 2 mg/l. The samples aliquots were then exposed to UV irradiation irregularly with the time periods of 10, 20, 30, 40, 50 and 60 minutes. The UV average pressure (irradiation intensity = 200 W/m2) lamp were applied in the reactor to conclude the quantity of Malathion prior and after the irradiation by HPLC instrument. In addition, the results obtained from the research were analysed using SPSS software and ANOVA and t-test statistical trials. Results: The least concentration dropped off took place at 10 min (46%) and the highestdecrease in 60 min (87.25%) (P<0.05)furthermore, the effectiveness of irradiation procedure is inversely proportional to the concentration of pesticide (P< 0.001). Nonetheless, the efficiency of the methodrises with increase in pH. Conclusion: The result data exhibits the most efficacies were achieved at pH= 9, at 60 min and 0.5 mg/l subsequently the application of UV reactors could be considered as asuitable method.