The use of pesticides and herbicides as a means of satisfying the nutritional needs of the growing world’s population has been extensively increased. On the other hand however, it has led to entry of a large amount of pollutants in soil and water resources: a serious threat to the environment. This study has focused on the seasonal biodegradation capability of atrazine herbicide, which can be found in Karun River sediments due to significant use in sugarcane farms. At first, sampling was conducted in both summer and autumn at the depth of 3 to 5 cm of river sediments. After enrichment, atrazine-degrading aerobic bacteria were isolated and identified by biochemical tests, and the results of two seasons were compared. Eight bacterial strains including Achromobacter insolitus, Delftia tsuruhatensis, Klebsiella pneumonia, Enterobacter ludvigjii, Serratia marcescens, Enterobacter sp., Bacillus sp., and Exiguobacterium profundum were identified. Based on the statistical analysis using SPSS software, ANOVA analysis, and Duncan test, a significant difference has been observed between the results of two seasons, the counted bacteria in summer showed to be 4.965±0.016 cfu/ml, larger compared with 4.894±0.017 cfu/ml in autumn. Most of atrazine-degrading bacteria were Gram-negative. The percentage of Gram-negative and Gram-positive bacteria in summer was determined 77% and 23% respectively, whereas no Gram-positive bacterium was found in autumn. Seasonal temperature change showed a significant impact on the number of bacteria in both seasons. The final results also indicated that the identified bacteria are effective selections for atrazine bioremediation in the environment.