In this study, we investigated the effects of supplemental polysaccharide (GCP) on growth performance and intestinal health of weaned piglets. Ninety piglets weaned at 28 days of age were randomly allocated to three groups with five replicates per treatment. Piglets were fed the following diets for 28 days: (1) CON (control group), basal diet; (2) G500, CON + 500 mg/kg GCP; (3) G1000, CON + 1000 mg/kg GCP. The results showed that supplementation with 1000 mg/kg GCP increased the average daily gain (ADG) and decreased the feed-to-gain ratio (F/G) ( < 0.05). Serum diamine oxidase (DAO) and D-lactic acid (DL-A) levels were lower in the G1000 group ( < 0.05). Dietary GCP 1000 mg/kg improved mucosal trypsin activity in the duodenum, jejunum and ileum and increased lipase and amylase activity in the jejunum ( < 0.05). Moreover, in the G1000 group, ZO-1, claudin 1 and occludin levels were increased in the jejunum mucosa, whereas interleukin-1β (IL-1β) and IL-6 levels were decreased ( < 0.05). The 16S rRNA gene analysis indicated that dietary 1000 mg/kg GCP altered the jejunal microbial community, with increased relative abundances of beneficial bacteria. In conclusion, dietary GCP 1000 mg/kg can improve growth performance, digestive enzyme activity, intestinal immunity, barrier function and microbial community in weaned piglets.