The purpose of this study was to investigate the protective effect of dietary conjugated linoleic acid (CLA) on the prevention of aflatoxin B-1 (AFB(1)) toxicity in the broiler chicken. A total of 99 Ross 308 male broiler chicks was assigned to nine treatments for 42 d. The experiment had a 3 X 3 factorial arrangement of treatments involving 0, 2 and 4 g CLA/kg feed, and 0, 200 and 300 ng AFB(1)/kg feed. The parameters evaluated, were feed. intake, body weight gain, feed efficiency, mortality, relative weights of liver and serum levels of total protein, total albumin, uric acid, alkaline phosphatase (ALP), aspartate aminotransferase (AST) and alanine aminotransferase (ALT). Aflatoxin B, in the diet negatively affected body weight gain and feed efficiency parameters when the birds were 21 and 42 days of age. Altered serum biochemical or hematologic measurements induced by AFB(1) treatments included increased serum activities of ALP, AST and ALT, decreased serum concentrations of albumin, total protein and uric acid. Liver weight was increased in birds given AFB(1) contaminated diet. The results indicated that CLA alone had insignificant effects on all parameters tested. However, birds receiving CLA+AFB(1) had a significantly higher body weight gain on day 42 than groups receiving AFB(1) alone. In addition, co-treatment with AFB(1) and CLA resulted in a significant improvement in feed efficiency and decreased relative weight of liver as compared with the AFB(1) groups. These results suggest that CLA provided protection against negative effects on liver damage induced by AFB(1) in broiler chickens.