This study was conducted to investigate the effect of diet including aflatoxin B1, thyme oil, and their combination on productive performance, nutrient digestibility, and carcass criteria of broiler chickens. A total of 192 one-day-old, unsexed broiler chickens (Ross 308) were divided into four treatment diets. Each treatment included 6 replicates (8 birds per each). During the period from 11-20 days of age, the birds were fed a basal diet without any supplementation (Negative control group; NC), a basal diet supplemented with aflatoxin B1 at 40 μg/kg in (positive control; PC), positive control diet supplemented with thyme oil at 200 mg/kg (Treatment 1; T1) and negative control diet supplemented with thyme oil at 200 mg/kg (Treatment 2; T2). The results indicated that supplementation of a combination of aflatoxin B1 at 40 µg/kg to broilers diet significantly (P<0.05) reduced body weight gain during the period of from 21-30 d and 1-38 days of age compared to other treatments. Thyme oil supplementation dramatically improved body weight, body weight gain and feed conversion ratio compared to other treatments. Regarding feed intake, nutrient digestibility, and carcass parameters, there were no appreciable variations between treatments. It could be concluded that thyme oil can reduce the negative impact of aflatoxin B1 in broiler diets.