The lung is one of the most common sites for cancer metastasis.Collagens in the lung pro-vide a permissive microenvironment that supports the colonization and outgrowth of disseminated tumor cells.Therefore,down-regulating the production of collagens may contribute to the inhibition of lung metastasis.It has been suggested that miR-29 exhibits effective anti-fibrotic activity by negatively regu-lating the expression of collagens.Indeed,our clinical lung tumor data shows that miR-29a-3p expression negatively correlates with collagen I expression in lung tumors and positively correlates with patients\'outcomes.However,suitable carriers need to be selected to deliver this therapeutic miRNA to the lungs.In this study,we found that the chemotherapy drug cisplatin facilitated miR-29a-3p accumulation in the exosomes of lung tumor cells,and this type of exosomes exhibited a specific lung-targeting effect and promising collagen down-regulation.To scale up the preparation and simplify the delivery system,we designed a lung-targeting liposomal nanovesicle(by adjusting the molar ratio of DOTAP/cholesterol-miRNAs to 4:1)to carry miR-29a-3p and mimic the exosomes.This liposomal nanovesicle delivery system significantly down-regulated collagen I secretion by lung fibroblasts in vivo,thus alleviating the establishment of a pro-metastatic environment for circulating lung tumor cells.