This study was carried out to investigate the effects of adding baker yeast (BY), chlortetracycline (CTC) and both BY + CTC to a control diet containing 200 ng/g of aflatoxin B I (C + AFB,)on performance, serum parameters and pathologyc alterations of broilers. A total 100chicks (Ross PM 3) were divided into five groups in individual cages and each containing 20 animals. BY, a rich source of protein and vitamin B complex, was mixed into the diets at 2.0 %, CTC was mixed into the diet at 2.5 ng/g. Feed consumption, body weight and feed efficiency were recorded weekly. Serum parameters and pathologyc alterations were determined at the end of the study. Dead animals were recorded daily. Liver changes were clearly apparent in the C+AFB(1), and C+AFB(1),+CTC most of the livers were enlarged, yellow and had pethecial hemorrhages. Canalicula cholestosis was absent in group C+AFB(1), and C+AFB(1) +CTC, but not others. When compared to the control (C) group, alkaline phosphatase (ALP), appear to be significantly increased in the C+AFB(1) and C+CTC+AFB(1) groups. Serum glutamic oxalacetic transaminase (GOT)was increased in C+AFB(1) birds. Serum alphaphetoprotein was not affected by the treatments. Feed consumption and body weight were significantly reduced in group AFB(1). Birds receiving BY + AFB(1),(,) CTC + AFB, and BY + CTC + AFB(1) had a significantly higher body weight than group C+AFB Feed efficiency was better in group CTC + AFB, than the others. The findings of this research suggest tha BY (2%) can partly counteract some of the toxic effects of AFB.