We sought to explore the treatment effects and the repair mechanisms of bone marrow derived mesenchymal stem cells (MSCs) during HCl-induced acute lung injury (ALI).MSCs were delivered through the tail veins of rats 24h after intraperitoneally injection of paraquat.The results showed that MSCs did not ameliorate the histopathologic changes of ALI and pulmonary fibrosis.We found that the activated Wnt/β-catenin signaling may regulate the differentiation of MSCs and is associated with lung fibroblasts activation, pulmonary fibrosis and tissue repair process in ALI rats.