Fe3O4 nanoparticles with high saturation magnetization were synthesized by thermal decomposition method using an inexpensive surfactant/reductant with short reaction time. The reaction time, temperature dependence on structure, morphology, magnetic property as well as magnetic heating effect of samples were characterized. The structural analysis showed that the Fe3O4 nanoparticles were of good crystallinity. TEM and FESEM images also revealed that the as-synthesized nanoparticles were quasi-spherical in shape and fairly uniform in size. The saturation magnetization of as high as 78 emu/g was obtained for Fe3O4 nanoparticles synthesized at 298 °C with mean particle size of 13 nm. The highest temperature (59.5 °C) was obtained for the sample of concentration of 5 mg/ml when applying an alternative magnetic field amplitude of 80 Oe and frequency of 178 kHz. Our results suggest that the obtained Fe3O4 nanoparticles be promising for applications in hyperthermic cancer treatment and MRI enhancement.