Monodispersed hollow Fe3O4 spheres with different diameters and shell thickness were synthesized by a simple solvothermal process and were investigated as anode materials for lithium ion batteries (LIBs). The shell of the hollow spheres exhibited porous structure composed of aggregated Fe3O4 nanoparticles. The composition and morphology of the obtained samples were characterized by X-ray powder diffraction (XRD), Raman spectra, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). A novel formation mechanism was proposed based on the results of time-dependent reactions. The electrochemical tests of the hollow Fe3O4 spheres were performed to determine the reversible capacity, rate and cycling performance as anode materials for LIBs. The Fe3O4 obtained from the reaction at 200°C for 48h exhibited the best specific capacity and capacity retention and superior rate performance compared to other Fe3O4 spheres, which is ascribed to their reasonable particle size, high crystallinity and hollow spherical structures. Different conductive additive were used to investigate the electrochemical performance of Fe3O4 hollow spheres. The binary conductive additives containing acetylene black (AB) and carbon nanobutes (CNTs) improved the electrochemical performance of the Fe3O4 hollow spheres obviously. The results reveal that there is a synergistic effect of the particle size, crystallinity and conductive agents on the electrochemical properties of the hollow Fe3O4 spheres.