Fe3O4 nanoparticles were synthesized by microwave combustion method by using thiourea as stabilizer. The synthesized Fe3O4 nanoparticles were characterized by powder XRD, HR-SEM, HR-TEM, EDX, PL and VSM studies. XRD results showed the well-crystalline cubic spinel structure of synthesized Fe3O4 nanoparticles with size of 49 nm. The morphology of Fe3O4 nanoparticles was confirmed by HR-SEM and HR-TEM images. In room temperature PL studies exhibited a strong UV emission and a suppressed green emission indicated the good crystalline properties for Fe3O4 nanoparticles. The magnetic behaviors reveal that the modification can decrease the saturation magnetization of Fe3O4 nanoparticles due to the surface effect.