Effects of a commercial probiotic, Bacillus cereus toyoi on abdominal fat accumulation in the Japanese quail fed either a commercial control diet (crude protein (CP), 23.5%; metabolizable energy (ME), 11.7MJ/kg) or a high-energy diet (CP, 23.0%; ME, 13.8MJ/kg) were investigated. Four-week-old male birds ( n = 108) were divided into four diet groups: control diet, control with probiotic, high-energy diet and high-energy diet with probiotic. At 8 weeks and 12 weeks of age (4 and 8 weeks of probiotic supplementation period, respectively), abdominal fat, muscles and the liver were weighed. The weight of total fat and protein in the muscles and liver were also determined. A rectal temperature was recorded weekly. Bodyweight and feed intake in both diets were not affected by probiotic supplementation. At 8 weeks of age, birds fed the control diet with probiotic had significantly less abdominal fat than those fed without the probiotic, and a similar tendency was seen for both diet groups at 12 weeks of age. The decrease in abdominal fat coincided with an increase in rectal temperature. These results suggest that greater metabolizable energy was consumed through elevation of heat production by supplementation of B. cereus toyoi , with hardly any energy stored as body fat. Probiotic supplementation appears to induce greater muscle weight, higher protein and lower lipid content in muscles by 8 weeks of age, and lower lipid content in muscles and greater liver weight by 12 weeks of age, in the Japanese quail.