SnO2 is considered as a promising anode material in lithium-ion batteries (LIBs). However, limited work has been focused on tensile mechanical properties and fracture mechanisms of lithiated and delithiated SnO2-based nanomaterials, which is of critical importance for the reliability of LIBs. In this study, in-situ tensile test performed in scanning electron microscope is employed to quantitatively study the tensile fracture of these electrochemically modified SnO2 nanowires (NWs). It is found that the lithiation-delithiation processes can cause a phase transition from crystalline to composite structure, leading to an obvious increase in fracture strain accompanied by plastic deformation, as compared to pristine SnO2 NWs. Meanwhile, the fracture strength and Young's modulus of SnO2 NWs were dramatically reduced. Interestingly, mechanical properties of delithiated SnO2 NWs are generally higher than those of lithiated ones. A finite element model was established based on a linear elastic-to-plastic hardening law to predict the tensile mechanical behaviors of lithiated and delithiated SnO2 NWs. The fitting results are in good agreement with experimental data. This work provides a basic understanding of mechanical characteristics of SnO2-based nanomaterials for LIBs applications.