To investigate the effects of glutamine（Gln） on expression of antibacterial peptide PR-39 mRNA in weaned piglets. Sixty four 28-day-old weaned piglets （Duroc×Landrace×Yorkshire） with an initial body weight of (7.50±0.67) kg were randomly allocated to two groups (control group and 1.0% Glnadded group) with four replicates in each group of eight per replicate (half male and half female). On day 28, the levels of IL-1β, IL-6 and TNF-α were analysed. On day 30, the effects of Gln on expression of antibacterial peptide PR-39 mRNA were determined by semiquantitative RT-PCR. The results indicated that, the level of IL-1β in serum increased significantly (P<0.05) with Gln addition, however, the levels of IL-6, TNF-α in serum and TNF-α, IL-2 in mucosal of jejunum were not significant affected with Gln addition compared with control group (P>0.05); the relative expressions of PR-39 mRNA in femur marrow and mucosal of jejunum significantly increased by 50.5% (P<0.05) and 24.0% (P<0.05), respectively. It was concluded, addition of Gln to diets for weaned piglets could significantly increase relative expression of PR-39 mRNA in both femur marrow and mucosal of jejunum.