The influences of dietary aflatoxin B1 on performance, on hematologic, pathologic and immunologic changes in broiler chickens were studied. One hundred and fifty hatched broiler chickens were fed with diet containing aflatoxin B1 (1.0 ppm and 2.5 ppm) fot three weeks. Blood samples, serum, and immune organs were obtained to investigate hematological, clinico-chemical, and histopathologial changes. Body weight gain and feed intake were significantly decreased. The liver and kidney were increased, whereas the bursa of Fabricius, spleen and thymus were decreased.