We evaluated the effect of dietary Aspergillus oryzae extract on gene expression profiles in the Longissimus lumborum from finishing steers. Cross-bred (Simmental × Angus) yearling steers were randomly assigned to one of 2 groups (n = 10/treatment). From receiving until d21, starter and step-up diets were fed to acclimate steers to a traditional mid-west finishing diet. Steers were then fed ad libitum to meet or exceed NRC requirements until slaughter (d140): basal diet with or without 5 g/hd/d of A. oryzae extract (Amaize, Alltech Inc., Nicholasville, KY) containing α-amylase (AMZ). On d90, Longissimus lumborum tissue was collected for gene expression analysis. Serum was collected at d 40, 90 and 140 for analysis of metabolites (BHBA, glucose, insulin, urea). Data from blood metabolites was analyzed using a mixed model. Gene expression was profiled using the Affymetrix Bovine Gene 1.0 ST Array. Performance did not differ between treatments. Hierarchical clustering indicated a treatment effect (P < 0.05) of the AMZ-supplemented group compared with the control. A total of 1148 genes were differentially affected (P < 0.05; 430 upregulated; 718 downregulated) between treatments. The genes affected, enriched (P < 0.05) and activated several pathways, including IGF-1 signaling, insulin receptor signaling, valine degradation, and VDR/RXR activation. The pathways activated are involved in the regulation of muscle development and growth. Blood metabolites indicated greater levels of BHBA, urea and insulin (P < 0.05) at d40 in AMZ-supplemented steers. Only insulin remained at a greater concentration in the AMZ group than the control throughout the experiment. In conclusion, AMZ supplementation in the finishing diet affects muscle gene expression and insulin metabolisms, potentially causing a positive effect for the development of skeletal muscle in finishing steers.