Fifteen multiparous Friesian cows with average live body weight (LBW) of 500±4.35 kg and 2-4 lactations were used after parturition and continues until 120 days of lactation and divided into three similar groups. Cows were fed a basal ration contained (DM basis) 40% concentrate feed mixture , 35% corn silage  and 25% rice straw  without any supplement in R1 (control) or orally supplemented with Chlorella algae and their media at the levels of 2 ml  or 4 ml per kg LBW to instead of 1 and 2 liter/head/day for R2 and R3, respectively. Results showed that nutrients digestibility and feeding values improved significantly (P<0.05) with increasing the level of supplementation. Addition of C. vulgaris increased (P< 0.05) feed intake, the concentrations of total protein and globulin, AST to ALT ratio in serum, actual milk, 4% fat corrected milk yield, milk contents, also TVFA's compared with the control. However, the concentration of NH₃-N and Live enzymes activity decreased. Whereas, ruminal pH value and serum albumin and creatinine concentrations were nearly similar for the different groups. Chlorella supplementation had a significant improvements in feed conversion, economic efficiency and post-partum reproductive traits compared to control group. In conclusion, cows supplemented with Chlorella and their media at the level of 4 ml/kg LBW showed the best results concerning productive and reproductive traits and economic efficiency.