Two experiments were conducted to investigate the effect of dietary supplementation with alpha-galactosidase preparation and stachyose on growth performance, nutrient digestibility and intestinal bacterial populations of piglets. In Experiment I 72 crossbred piglets were allotted to three treatments, i.e. 1) control (basal) diet, 2) alpha-Gal1 and 3) alpha-Gal5, the basal diet supplemented with 0.01% and 0.05% alpha-galactosidase preparation (alpha-Gal), respectively. Average daily gain, average daily feed intake and feed conversion ratio were not influenced by alpha-Gal supplementation. In Experiment II 72 crossbred weanling piglets were randomly assigned to four treatments with a complete factorial design, i.e. 1) basal diet, 2) basal diet with 0.01% alpha-Gal supplementation, 3) basal diet with 1% stachyose supplementation and 4) basal diet with 1% stachyose and 0.01% alpha-Gal supplementation. Average daily gain and feed conversion ratio were influenced by alpha-Gal and stachyose supplementation. The ileal digestibility of stachyose, raffinose, gross energy and crude protein was improved significantly by alpha-Gal supplementation. The microbial populations in the intestine were modified by both alpha-Gal and stachyose supplementation. The data suggested that stachyose supplementation had an adverse effect on the growth performance of piglets and alpha-Gal supplementation could ameliorate it, especially in younger pigs.