Chlorella pyrenoidosa has been used safely in humans and in other animals as an immune stimulant. The aim of this study was to evaluate the dietary supplementation with Chlorella pyrenoidosa to ameliorate the effects of subacute intoxication with aflatoxin B₁ (AFB₁) in broiler chickens. Hepato-protective assessment of 7-d-old chicks was performed on a total of 120 chickens (Hubbard) divided into six groups having two replicates with 10 birds each: Control, AFB₁ (350 ppb), Chlorella pyrenoidosa ethanolic extract (CP) at 250 mg; 500 mg and co-treatment of CP (250 mg; 500 mg) and AFB₁. The experiment was conducted for 35 days. The contents of AFB₁ and AFB₁+CP diets were 350 ppb throughout the experimental period. The results indicated that diet contaminated with low level of AFB₁ significantly (P<0.05) reduced the average weight gain and daily food intake during the entire experiment and decreased (P<0.05) the serum contents of total protein, albumin and globulins. Moreover, a dietary low level of AFB₁ not only increased (P<0.05) lipid peroxidation but also reduced (P<0.05) total antioxidant capability, catalase, glutathione reductase and peroxidase activity in liver. Furthermore, addition of CP (500 mg) to AFB₁ contaminated diet counteracted these deleterious effects, indicating that supplementation of Chlorella pyrenoidosa to the broiler diet was safe, quiet cheaper provides 16% cost benefit ratio as compared to standard feed supplement, promoting beneficial effects (500 mg) in poultry health with respect to the toxic effects of 350 ppb diet.