Background & Objectives: Surfactants are organic chemical compounds that increase cleaning power of water through reducing surface tension. Linear alkyl benzene sulfonate (LAS) as an anionic surfactant may cause environmental problems especially eutrophication phenomenon in surface waters. The purpose of this study is to evaluate efficiency of extended aeration process in removal of LAS in Paveh city. Methods: This descriptive cross-sectional study was carried out for 12 months in 2008. Sampling was done at 8:00 am, 10:00 am, and 12:30 pm. Methylene blue method was used to determine LAS. In total, 108 samples were taken from inlet, outlet, and return sludge during the study. All the sampling and testing methods were performed according to standard method guidelines. Results: The results showed that efficiency of the system in removal of LAS, COD, and TSS in the warm seasons (i.e. April to September) were significantly higher than the cold seasons (p<0.001). According to the results, the average of LAS removal in winter and summer were 94.06% and 99.23%, respectively. Respective values for removal of COD and TSS were 89.1% and 72.1% in winter and 91.06% and 76.36% in summer. In addition there was a direct relationship between COD and TSS parameters with LAS (R2=0.98). Conclusion: It can be concluded that Paveh wastewater treatment has high performance in removal of anionic detergent in different seasons. So that, the parameters measured in all seasons (except concentration of LAS in winter) met the standards set to agriculture and surface water discharges.