Objective To study the effect of mechanical stretch on pentraxin-3 (PTX3) expression and release in human alveolar epithelial cells(A549). Methods The cells grown on collagen 1 BioFlex plates were exposed to square cyclic stretch at 0.3Hz using the Flexercell system with 20% elongation of cells. After stretching for 1,2,4,6 hours, conditioned media were collected and the levels of PTX3 protein were measured by Western blotting. Real-time PCR of PTX3 mRNA extracted from stretched cells was performed. Apoptosis? and viability of the cells following treatments were routinely monitored. Results The results of this study showed that: 1) cyclic stretch led to increase gene expression and release of PTX3 from alveolar epithelial cells ;2 ) stretch induced apoptosis? in alveolar epithelial cells; 3) PTX3 levels correlated with severity of apoptosis of alveolar epithelial cells.C onclusion The above results suggest that PTX3 may act as an important mediator for tissue damage and play an important role for ventilator-induced lung injury