An experiment was conducted to evaluate the effects of dietary lactose alone or in combination with dried milk-yeast product on growth performance, gastrointestinal microbiota, and immune parameters in weanling pigs. Pigs fed lactose and lactose with milk-yeast tended (P = 0.07) to have greater BW compared to control pigs (19.56 and 19.60 vs. 18.55 lb) at the end of phase 1 (week 1 to 2); however, no differences in BW were observed during phase 2 (week 3 to 4), phase 3 (week 5), or overall (week 1 to 5). With respect to growth performance, pigs fed lactose and lactose plus milk-yeast had greater (P = 0.05) ADG, and tended (P = 0.07) to have greater ADFI compared to control pigs during phase 1. There were no differences observed for ADG or ADFI during phase 2, 3, or the overall experimental period. With respect to immune parameters, a main effect of treatment was observed for circulating immunoglobulin (Ig)A where control pigs had greater (P < 0.01) concentrations of IgA compared to pigs fed lactose with or without milk-yeast; however, no effects of dietary treatment were observed for circulating IgG or tumor necrosis factor alpha. Lastly, fecal microbiota of control pigs had a greater microbial diversity index (Shannon’s , P = 0.03) compared to pigs fed lactose plus milk-yeast on day 0; however, no differences in microbial diversity indices were observed on days 7 or 14 among dietary treatments. In addition , a shift in microbial composition, limited to a small number of microbial groups, was observed on day 7 with lactose fed pigs having greater (P = 0.05) putative L. jonhsonii staining intensity compared to control pigs and pigs fed lactose plus milk-yeast. On day 14, L. reuteri tended (P = 0.15) to be enhanced , and L. delbrueckii was virtually eliminated (P = 0.04) by feeding lactose with or without milk-yeast. This research indicates that growth performance, immune parameters, and composition of the fecal microbiota may be affected by dietary inclusion of lactose alone or in combination with milk-yeast.