Background/Aims: Previous studies have revealed that mast cells (MCs) may activate the protease-activated receptors and release of neuropeptides involved in the pathogenesis of irritable bowel syndrome (IBS). The levels of proteaseactivated receptor 2 (PAR-2) and tryptase can contribute to understanding the pathogenesis of IBS. Methods: Colonoscopic biopsies were performed of 38 subjects (20 with IBSdiarrhea [IBS-D], eight with IBS-constipation [IBS-C], and 10 healthy volunteers). The mRNA and protein levels of tryptase and PAR-2 were assessed by real-time PCR and Western blot. The levels of vasoactive intestinal peptide (VIP), substance P (SP), and calcitonin gene-related peptide (CGRP) were measured by immunohistochemistry, and MCs were counted by toluidine blue staining. Results: Significant increases in the mRNA expression of tryptase (p<0.05, IBS-D, IBS-C vs control) and PAR-2 (p<0.05, IBS-D, IBS-C vs control) and in the tryptase protein level (p<0.05, IBS-D, IBS-C vs control) were detected in IBS. Elevations of MCs, CGRP, VIP and SP (p<0.05, IBS-D vs control) were observed for IBS-D only. Conclusions: Tryptase levels may upregulate the function of PAR- 2, resulting in the release of neuropeptide and they were correlated with clinical symptoms associated with IBS. (Gut Liver 2016;10:382-390)