In this study locally isolated microalgae (Chlorella vulgaris Bejerinck) was used in wastewater treatment to reduce the pollutant parameters. Three parameters were studied to determine the efficiency of Chlorella vulgaris in reducing COD, BOD and PO4 concentration. Samples of wastewater were taken from a primary station in Al-Rustomiya wastewater treatment station. Three different dilutions of wastewater were tested; 100% waste, 75%waste 25%waste with distilled water. Chemical oxygen demand (COD) values started with 370mg/l, 270mg/l and 200mg/l for samples A, B and C respectively, and it reached after 14 days to 112 mg/l, 88 mg/l, and 120 mg/l. Biochemical oxygen demand (BOD) started with 241mg/l, 200mg/l, and 170 mg/l for samples A, B and C respectively, and it declined to 110 mg/l, 61 mg/l, and 112 mg/l. Finally PO4 started with 39.9 mg/l, 30 mg/l, 21 mg/l and it reached to 17.1mg/l, 8mg/l, 11.2mg/l for samples A, B and C respectively. Sample B showed the best removal values for COD, BOD and PO4 which reached to 88 mg/l, 61 mg/l, and 8 mg/l respectively.