The experiment was conducted to investigate the effect of Astragalus powder prepared by using different comminution techniques on growth performance and immune function of pigs. Duroc×Landrace×Yorkshire young growing pigs (n=90, female, 60 days of age, liveweight 21.88±1.26 kg) were randomly allocated to three treatments. Each treatment had three replicates with ten pigs per pen. The basal diets were not supplemented or supplemented (5 g/kg) with 80 mesh Astragalus (180 μm), or micron Astragalus (6.32 μm), respectively; the feeding experiment lasted 30 days. After completion of the feeding experiment, three animals from each treatment were chosen to determine the effect of Astragalus on immune function. Results showed that supplementation with micron Astragalus significantly increased (P<0.05) average daily gain (ADG), both Concanavalin (ConA) and lipopolysaccharide (LPS)-induced splenocyte and peripheral lymphocyte proliferation, and significantly increased (P<0.05) serum IgG, IgA, IL-1α and IL-2 concentrations compared with the control groups. Supplementation with 80 mesh Astragalus only increased (P<0.05) serum IgA, IL-1α and IL-2 concentrations compared with control. The results indicated that micron Astragalus was more effective than 80 mesh Astragalus in improving growth performance and enhancing immune function of pigs.