Background: Considering the severe health and environmental hazards caused by the entry of diazinon toxin into water resources, its removal is very important. Given the high costs of imported adsorbents, this research attempted to evaluate, for the first time, the efficiency of Iranian activated carbon in removing diazinon from aqueous solutions. Methods: In this batch experimental study, the effects of contact time (5-90 minutes), adsorbent concentration (0.5-30 g/L), initial concentration of diazinon (5-50 mg/L), and pH (3-10) on the adsorption of diazinon onto the activated carbon were evaluated. Concentrations of diazinon were measured using a high pressure liquid chromatography (HPLC) instrument. The specific surface area of the adsorbent was determined by BET and BJH methods. The experimental adsorption data was analyzed using Langmuir and Freundlich isotherm models. Pseudo first-order and pseudo second-order kinetics models were employed to determine kinetics. Moreover, data was analyzed using SPSS version 19, and Pearson correlation and analysis of variance (ANOVA) tests were performed at a significance level of 0.05. Results: The optimum contact time, sorbent dose, and pH were 30 minutes, 10 g/L, and 5, respectively. The adsorbent could adsorb diazinon with a removal efficiency of 92.5% under optimum conditions (initial concentration: 20 mg/L). The experimental data was better described by the pseudo-second order kinetic and Langmuir isotherm. A maximum adsorption capacity of 71.4 mg/g was calculated by the Langmuir isotherm model. Conclusion: With respect to the high adsorption capacity of Iranian activated carbon, this sorbent can be considered an efficient adsorbent for the removal of diazinon from aqueous solutions. Keywords: Diazinon, Adsorption, Activated carbon, High pressure liquid chromatography Citation: Akbarlou Z, Alipour V, Heidari M, Dindarloo K. Adsorption of diazinon from aqueous solutions onto an activated carbon sample produced in Iran.