The aim of present study was to evaluate the potential synergistic effect of salinomycin and nisin on gastrointestinal tract microbial ecology and activity as well as the influence of nisin on broiler chicken growth performance. In the first experiment, which lasted 35 days, such dietary additions as: NA – no additives, SAL – salinomycin (60 mg · kg⁻¹ diet), NIS – nisin (2700 IU · kg⁻¹ diet) were used. Nisin addition in comparison to salinomycin and control treatments, improved body weight gain in the entire experiment (days 1–35) as well as increased feed intake and decreased feed conversion ratio, but only in the starter period (days 1–14). In the second experiment the same dietary additions and also SAL+NIS – salinomycin and nisin (60 mg · kg⁻¹ diet and 2700 IU · kg⁻¹ diet, respectively) were applied. The results of the second experiment indicated that salinomycin and nisin combination decreased the total bacteria counts, as well as Enterobacteriaceae, Clostridium perfringens, Lactobacillus spp./ Enterococcus spp. and Clostridium coccoides–Eubacterium rectale cluster in the ileum. Furthermore, the interaction between applied factors was noticed in the decreasing total bacteria counts, Lactobacillus spp. Enterococcus spp., Clostridium coccoides–Eubacterium rectale cluster and increasing signals from Bifidobacterium spp. as well as Streptococcus sp. Lactococcus. There were no interactions between nisin and salinomycin in terms of organic acids concentration in the crop, gizzard, ileum and caecum, as well as pH value, except gizzard. The results of the present study have indicated the positive effect of nisin on broiler growth performance and the fact that nisin and salinomycin can act synergistically in scope of ileal microbiota ecology modification.