Growth promoters are additives used in animal nutrition to improve productivity. Most of them are antibacterial products and coccidiostats that are used therapeutically until just before slaughter. Restrictions on the use of antibiotics introduced by the EU along with consumer demand for products without antimicrobial residues have led manufacturers to find alternatives. Probiotics are products of living microorganisms that have a beneficial effect on the host, improving the intestinal microbial balance. They improve feed utilization with a tendency to increase their use in mixtures because they do not leave residues in the environment, the animal's body and do not cause resistance in humans compared to antibiotics. Therefore, the aim of this work was to determine the effect of probiotics based on Bacillus subitus on production results and slaughter indicators of chicken carcasses. The experiment was conducted on 240 Ross 308 hybrid chickens divided into two groups, control and experimental, with 40 g/t of probiotics (Bacillus subtilis DSM 28343). Chicken weight, consumption and mortality were monitored throughout the fattening period, and body weight gain and conversion were calculated. After 35 days, 20 chickens of each group, carcass slaughter indicators were determined (randman; proportions of wings, drumsticks, rumps, breast, fillet, back, and abdominal fat, stomach and liver mass). The use of probiotics, Bacillus subtilis, in broilers resulted decrease in average body weight and growth. Chickens that received the probiotic achieved 18% more abdominal fat and higher feed conversion compared to the control. Based on the obtained results, we conclude that the addition of probiotics to feed mixtures for broilers, in a standardized production method, does not improve the production results of chickens for fattening. However, further research is needed on the effect of probiotics as an alternative to antibiotics and their impact on the health and production performance of broiler chickens.