This study was carried out to determine the effects of Bacillus subtilis addition to growing Japanese quail diets on growth performance, some serum parameters and carcass parameters. In the study, a total of 200 mixed-sex Japanese quail (Coturnix coturnix japonica) chicks were fed for 35 days with diets formed with the addition of different levels of control and Bacillus subtilis (250, 500, 750 mg/kg). The study was carried out in 4 treatment groups with 5 replications. At the end of the experiment, Bacillus subtilis levels did not affect the feed intake and feed conversation ratio, which are performance parameters, but affected the body weight and body weight gain statistically significantly. The addition of Bacillus subtilis to the diets of growing Japanese quails showed that glucose and creatinine concentrations were significantly affected, and urea, triglyceride, cholesterol, total protein, phosphorus and calcium values were not affected by the treatment levels. Among the carcass parameters, carcass yield, liver weight, pancreas weight, heart weight, gizzard weight and intestinal length did not statistically differ between the treatment groups. According to the results of the present study, it can be said that the addition of Bacillus subtilis at the level of 500 mg/kg to growing quail diets may be beneficial in terms of improving performance.