Abstract: The experiment was conducted to study the effects of the addition of encapsulated and nonencapsulated compound acidifiers in a diet based on cornsoybean mealextruded soybean on gastrointestinal pH, growth performance, villus height and crypt depth of jejunum, intestinal digestive enzymes activities, microbial population and intestinal mucosal secretory immunoglobulin A (SIgA) in weaning piglets. Sixtyfour 28dayold, crossbred piglets (Landrace×Large White), weighing an average of (7.00±0.10) kg, were randomly assigned into four treatments with four replicates and four piglets (2 male and 2 female) per pen, according to singlefactor design principle. The feeding trial lasted for 35 days. The results showed that microcapsule slowrelease compound acidifiers significantly reduced the pH in stomach and small intestine（P<001）. In addition, microcapsule slowrelease compound acidifiers significantly increased the ratio of the villus height to crypt depth of jejunum（P<001）, and stimulated the sucrase activity and lactase activity in the early weaning period（P<005）as well. During the later weaning period, microcapsule compound acidifiers significantly increased the counts of lactobacillus and decreased the counts of Escherichia coli in the cecum and the colon（P<001）. It was also noted that there was an tendency of lower secretion of intestinal mucosal secretory IgA（P>005）. These results indicated that the microcapsule slowrelease compound acidifiers could optimize the intestinal microflora and improve the intestinal morphology and function by reducing the gastrointestinal pH, so as to enhance the intestinal digestibility and adaptation, and consequently improve the growth performance in weaning piglets.