Fe3O4 nanocrystals were synthesized with polyethylene glycol (PEG) and polyvinyl pyrrolidone (PVP) as dispersant respectively by solvothermal process. The nanocrystals were characterized in order to elucidate the morphology and structure by transmission electron microscopy (TEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) respectively. The results indicated that Fe3O4 nanocrystals were cubic phases, and the morphologies of samples were globular nanoparticles structure no matter what dispersant was. The photocatalytic degradation of levofloxacin lactate (LVFX) revealed that Fe3O4 nanocrystals promoted the degradation of LVFX. As the UV radiation time was only 30 min, the photocatalytic degradation percentage of LVFX with Fe3O4 (magnetite) as catalyst was about 92%. However, the direct photolysis degradation percentage of LVFX without Fe3O4 is about 85%.