The in-situ mechanical properties of Fe3O4 nanowires (NWs) of a magnetic material grown by an oxide assisted vapor-solid processes are experimentally investigated. Investigations are carried out with a nano-tensile testing technique via a custom-made nanomanipulator inside the SEM. The modulus of elasticity, yield stress and fracture stress of Fe3O4 NWs are estimated to be 23.8 +/- 3.8 GPa, 428 +/- 55 MPa and 1.10 +/- 0.29 GPa, respectively. Strain range at breaking of NWs is obtained as 5% to 11%. The results indicate that the Fe3O4 NWs have highly malleable and stretching properties.