This study was conducted to investigate the expression of atrogin-1/MAFbx, a muscle-specific ubiquitin ligase, in the smooth muscle of the chicken gizzard. Atrogin-1/MAFbx mRNA expression was detected in the skeletal muscle, heart (cardiac muscle), gizzard (smooth muscle), brain, and liver of chicks, with highest expression in the smooth muscle of the gizzard. The expression of atrogin-1/MAFbx mRNA in the smooth muscle of the gizzard was increased by fasting (24 h), and this increase was reduced by refeeding (2 h). These results indicate that atrogin-1/MAFbx mRNA is highly expressed in the smooth muscle of the chicken gizzard, and that the expression of it is regulated by nutritional conditions.