— Water contamination has become a major concern in current societies. Wastewater treatment plants has been instructed and operated with the aim of water pollution reduction. Carrousel oxidation ditches are known as an efficient system for removal of nutrients and organic matter. In the present study, a wastewater treatment plant located in Iran was investigated in terms of wastewater treatment. The results were reported in summer and winter. The average removal efficiency of COD was 93.92% and 90.77%, in summer and winter, respectively. The average influent and effluent of total phosphor was 6.28 and 3.48 mg/L in summer and 6.20 and 4.14 mg/L, respectively. The average effluent TSS concentration in winter and summer were 22.06 and 13.05 mg/L, respectively. The average total Kjeldahl nitrogen removal efficiencies of summer and winter were 93.05% and 91.41%, respectively. In summary, carrousel oxidation ditches were suitable for pollutants removal and a bit higher efficiency was attained in summer than winter.