A study investigated the effects of Galla Rhois (GR) on growth performance and diarrhea incidence of postweaning piglets. One hundred 28-day-old piglets were randomly assigned into five experimental groups, which were a basal diet alone (NC), chlortetracycline 0.3 g/kg feed (PC) and supplemented with GR 1.0 g/kg feed (GR 1), GR 2.0 g/kg feed (GR 2), and GR 4.0 g/kg feed (GR 3). After 28 days of administration, final body weight (BW) and feed conversion ratio of PC, GR 2 and GR 3 was significantly different compared to those of NC (p < 0.05). Additionally, the average daily gain (ADG) and average daily feed intake (ADFI) of PC and all groups treated with GR was significantly different compared to those of NC (p < 0.05). Especially, final BW, ADG, ADFI and feed conversion ratio (FCR) of GR 2 and GR 3 were not significant different compared to those of PC. In fecal scores and duration of diarrhea, PC and all groups treated with GR were significantly different compared to NC (p < 0.05). In hematogolical and serum biochemical analysis, there were no significant differences in any of the hematogolical and serum biochemical parameters examined in either NC or all groups treated with GR. The results of this study indicated that GR could be a potential candidate as feed additives for the improvement of growth performance and incidence of diarrhea in piglets.