The aim of this experiment was to determine the influence of humic substances or humic substances and thyme on carcass parameters of broiler chickens. A total of 60 Ross 308 broiler chickens were divided into 3 groups (n=20). The control group of chickens was fed with complete feed mixtures without any additives. Chickens in the first experimental group were fed a diet containing 1.5% of humic substances. Chickens in the second experimental group were fed a diet containing 1.5% of humic substances and 0.5% of thyme. In 42 day of fattening, 5 male and 5 females with body weight similar to the mean were chosen from each group of chickens. The carcass weight (g), the breast and thigh percentages (%), edible weight (g) and carcass yield (%) were recorded. We found statistical significant increase (P<0.05) of heart weight in the first experimental group in comparison with other groups. The favourable tendency of the effect of the supplements used, although without a statistically significant differences (P>0.05), was observed in both experimental groups in liver and gizzard weights. We recorded statistically non-significant differences (P>0.05) in carcass weight, carcass yield, breast a thigh percentage in the both experimental groups compared with control group.