Abstract  Quorum sensing system is a cell-to-cell communication system that plays a pivotal role in virulence expression in bacteria. Recent advances have demonstrated that the Pseudomonas aeruginosa quorum sensing molecule, N-3-oxododecanoyl homoserine lactone (3OC₁₂-HSL), exerts effects on mammalian cells and modulates host immune response. Mast cells (MCs) are strategically located in the tissues that are constantly exposed to external stimulus. Therefore, it is very much possible that 3OC₁₂-HSL may interact with MCs. Little is known, however, about specific effects of 3OC₁₂-HSL on MCs. To address this, we investigated the influence of 3OC₁₂-HSL on cell viability, apoptosis, intracellular calcium and cytokine release in MCs. We found that at high concentrations (100 μM), 3OC₁₂-HSL inhibited proliferation and induced apoptosis in P815. The 3OC₁₂-HSL treatment significantly increased intracellular calcium release in both P815 and HMC-1. We also observed that 3OC₁₂-HSL-induced histamine release and degranulation in HMC-1 cells. Furthermore, 3OC₁₂-HSL-induced IL-6 production at lower concentrations (6.25–12.5 μM) but steadily reduced IL-6 production at high concentration (50–100 μM). These data demonstrate that P. aeruginosa 3OC₁₂-HSL affects MCs function.