Fe3O4 nanoparticles are fabricated by two hydrothermal and thermal decomposition methods. The hydrothermal method is synthesized in a water solvent while the thermal decomposition method is synthesized in an organic solvent. The structure, morphology and magnetic properties of the powder and magnetic liquid samples were investigated on modern equipment. Analysis results on X-ray diffraction spectroscopy (XRD) showed that the resulting particle systems have single phase structure of spinel ferrite. From the scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) images, the particles can be spherical, the size is quite uniform. The average particle size of the samples fabricated under the optimum conditions by the hydrothermal method (2 hours, 160 ° C) and thermal decomposition (2 hours, 298 ° C) were 15 nm and 13 nm, respectively. Values from the highest saturation (Ms) obtained are 63 emu / g and 70 emu / g for the above samples, respectively. Magnetic liquid samples used poly acrylic acid (PAA) as phase transition agent for high strength with zeta potential in the range of - 40 mV to -50 mV. Fluid system with good dispersion, high durability opens up good applicability in biomedical.