In the present study, we isolated Lactobacillus fermentum IM12 from human gut microbiota, which strongly inhibited interleukin (IL)-6 expression and STAT3 activation in lipopolysaccharide (LPS)-stimulated murine peritoneal macrophages, and examined its anti-inflammatory effect in mice with carrageenan-induced hind-paw oedema (CIE) or 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced colitis (TIC). Oral administration of IM12 (0.2×109, 1×109 or 5×109 cfu/mouse, once a day for 3 days) in mice with CIE significantly suppressed the increase of oedema volume and thickness, as well as myeloperoxidase activity and IL-6, IL-17, NO, and prostaglandin E2 levels in the carrageenan-stimulated paw. Treatment with IM12 (1×109 cfu/mouse, once a day for 3 days) in mice with TIC significantly suppressed colon shortening, and myeloperoxidase activity and IL-6 and IL-17 levels. Treatment with IM12 in mice with CIE or TIC also suppressed the expression of inducible NO synthase (iNOS) and cyclooxygenase (COX)-2, as well as activation of nuclear factor kappa beta (NF-κB) and signal transducer and activator of transcription 3 (STAT3). Furthermore, IM12 significantly inhibited the expression of iNOS, and COX-2, as well as activation of NF-κB in LPS-stimulated mouse peritoneal macrophages. The inflammatory effect of heat-inactivated IM12 was significantly different to that of live IM12 in mice with TIC, although anti-inflammatory effect of IM12 was reduced by heat treatment. Based on these findings, IM12 may attenuate inflammation by inhibiting NF-κB-STAT3 signalling pathway.