This study was performed to evaluate effects of Armillariella tabescens (A. tabescens) on the growth performance and intestinal immune response and microflora in early-weaned pigs when used as feed additive. A. tabescens mycelia were added to basal diets at concentrations of 0%, 0.1%, 0.3% or 0.9% (w/w). A total of 144 commercial cross-bred piglets were randomly allocated to one of these four diets and fed for 30 days. The growth performance of early-weaned piglets displayed improvement with diets containing 0.1% and 0.3% dried mycelia powder from A. tabescens. Supplementing with 0.1% or 0.3% A. tabescens mycelia induced a 2.6- and three-fold increase in secretory immunoglobulin A (sIgA) content in the jejunal mucosa, respectively, but had only a marginal effect on sIgA in the ileal mucosa. Expression of interleukin-2, interferon-γ, and tumor necrosis factor-α in the jejunal mucosa were elevated with A. tabescens mycelia administration. Increased amounts of Lactobacillus spp. and Bifidobacterium spp. in the jejunum, and decreased amounts of Escherichia coli in the jejunum and ileum were observed with the administration of A. tabescens-containing diets. This study demonstrated that A. tabescens had beneficial effects on the growth performance and intestinal microflora of early-weaned pigs.