Butoxybutyl alcohol (BBA) is a possible growth promoter contained in the fermentation and distillation by-products of a traditional Japanese spirit, shochu. In the present study, BBA was synthesized and its chemical structure was confirmed by gas chromatography mass spectrometry and nuclear magnetic resonance. Then, two studies were conducted to investigate the effects of feeding the synthesized BBA on the growth and skeletal muscle proteolysis of broiler chickens. Ross male broiler chickens were divided into two groups, control (basal diet: 219 g crude protein/kg and 12·66 MJ metabolizable energy/kg) and BBA diet (30 mg BBA/kg basal diet), with the experimental diets being provided from 15 to 27 days and 0 to 27 days of age, for Studies 1 and 2, respectively. Butoxybutyl alcohol supplementation increased final body weight in both studies, whereas feed intake was unchanged, thereby indicating significantly increased feed efficiency. Furthermore, the synthesized BBA increased the weights of the pectoralis superficialis and profundus muscles, and the leg. The BBA decreased the Nτ-methylhistidine concentration in the excrement and plasma, which are indices of the rate of skeletal muscle protein degradation. It also decreased the mRNA levels of μ-calpain large subunit, atrogin-1/muscle atrophy F-box (MAFbx), ubiquitin and 20S proteasome C2 subunit. These suggest that growth promotion due to the feeding of synthesized BBA is caused by the suppression of skeletal muscle protein degradation, which is related to a decrease in gene expression in the calpain and ubiquitin–proteasome systems.