Objective To investigate the effect and mechanism of osteosarcoma exosomes on tumorassociated fibroblast transformation.Methods The exosomes of osteosarcoma cells U2-OS, Mg-63 and human osteoblasts hfob1-19 were extracted and identified. The exosomes of PBS, hFoB1-19, U2-OS and Mg-63 were incubated with human lung fibroblasts MRC-5. The proliferation ability of MRC-5 was detected by CCK8 method, the migration and invasion ability of MRC-5 was detected by Transwell chamber method, and the inflammatory factor IL-1 in MRC-5 cells was detected by QRTPCR-β、The expression of IL-6 and IL-8 was detected by Western blot-α The expression of SMA, vimentin and FAP, and the activation of JAK2/STAT3 signaling pathway. Results he exosomes were identified by transmission electron microscope and Western blot. When CO incubated with U2-OS and Mg-63 exosomes, the proliferation, migration and invasion of MRC 5 increased significantly; IL-1β, IL-6 and IL-8 in MRC 5 increased significantly; the expressions of α-SMA, vimentin and FAP were significantly increased, and the phosphorylation levels of JAK2 and STAT3 were significantly increased (all =P＜0.001). Conclusion Osteosarcoma cell exosomes promote the transformation of fibroblasts into tumor-associated fibroblasts by activating JAK2/STAT3 signaling pathway.