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 B1 (C + AFB1) on performance, serum parameters and pathologyc alterations of broilers. A total 100 chicks (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+AFB1and C+ AFB1+CTC most of the livers were enlarged, yellow and had pethecial hemorrhages. Canalicula cholestosis was absent in group C+AFB1 and C+ AFB1+CTC, but not others. When compared to the control (C) group, alkaline phosphatase (ALP), appear to be significantly increased in the C+AFB1 and C+CTC+ AFB1 groups. Serum glutamic oxalacetic transaminase (GOT)was increased in C+AFB1 birds. Serum alphaphetoprotein was not affected by the treatments. Feed consumption and body weight were significantly reduced in group AFB1. Birds receiving BY + AFB1, CTC + AFB1 and BY + CTC + AFB1 had a significantly higher body weight than group C+AFB1. Feed efficiency was better in group CTC + AFB1 than the others. The findings of this research suggest tha BY (2%) can partly counteract some of the toxic effects of AFB1.