Eight Holstein dairy cows (4 primiparous and 4 multiparous) were used in a replicated 4×4 Latin square design with four 21-d periods to investigate effects of xylose-treated soybean meal (XSBM) as a source of ruminal undegradable protein in early lactation cows fed barley-based diets. Treatments were diets with XSBM ratios of (1) 0% (control), (2) 4.5%, (3) 9% and (4) 13.7%5, on a dry matter DM basis. Milk production, 4%FCM, milk energy, milk protein, lactose, solids-non-fat and total solids yield were increased by feeding XSBM. Milk fat, protein, lactose, solids-non-fat and total solids percent were not different among treatments. Intake of dry mater, crude protein and energy, blood glucose, albumin and total protein, rumen, fecal and urine pH and changes in body weight were not affected by treatments. Feed, crude protein and energy efficiency were improved by substitution XSBM for soybean meal but not by parity. Increasing dietary XSBM in the ration reduced blood urea N. Results of this study showed that increasing dietary XSBM ratio improved milk production in early lactation cows fed diets based on barley.