The present study was conducted to investigate the effects of xylo-oligosaccharide (XOS) on plasma biochemical indices, amino acid contents and fiber type composition of muscle of growing-finishing pigs. A total of 80 Duroc×Large White×Landrace pigs with an initial body weight of about 30 kg and at 70 days of age were randomly assigned to 8 groups with 10 replicates per group (half male and half female) and one pig in a replicate. The eight groups included control group, antibiotic group, supplementation groups of 100, 250 and 500 g/t XOS during 30 to 65 kg stage, and supplementation groups of 100, 250 and 500 g/t XOS during 30 to 100 kg stage. When the average body weight of pigs reached about 100 kg, blood samples were collected by precaval vein, and then the plasma were obtained for analyzing biochemical indices. The samples of longissimus dorsi (LD) muscle were collected and the contents of amino acids, mRNA expression levels of muscle fiber types and muscle growth-related genes were measured. The results showed as follows:1) compared with the control group or antibiotic group, dietary supplementation with different doses of XOS significantly increased plasma globulin content and significantly decreased the ratio of albumin to globulin (P<0.05); 2) compared with the control group or antibiotic group, during 30 to 65 kg stage, dietary supplementation with 250 g/t XOS significantly decreased the contents of threonine (Thr), leucine (Leu), phenylalanine and serine (Ser) in LD muscle (P<0.05), and dietary supplementation with 500 g/t XOS significantly increased the mRNA expression levels of myosin heavy chain Ⅱx (MyHCⅡx), myogenic determination factor (MyoD), myogenin (MyoG) and muscle cell enhancement factor 2A (MEF2A) in LD muscle (P<0.05); 3) compared with the control group or antibiotic group, during 30 to 100 kg stage, dietary supplementation with 100 or 500 g/t XOS significantly increased the contents of Thr, Leu, Ser, total amino acids, essential amino acids and flavor amino acids, as well as the mRNA expression levels of MyHCIⅡx, MyoD, MyoG, MEF2A and myostatin in LD muscle (P<0.05). Collectively, these findings suggest that dietary supplementation with suitable doses of XOS can regulate nitrogen metabolism and up-regulate the expression levels of muscle fiber type and muscle growth-related genes, and the efficiency of dietary supplementation with 100 g/t XOS is optimal for pigs with 30 to 100 kg body weight.