The Fe 3 O 4 nanoparticles were synthesized by a coprecipitation method, and their particles were capsulated by 3-thiopheneacetic acid (3TA), 2, 3-meso-dimercaptosuccinic acid (DMSA) and Polyethylene glycol (PEG), respectively. The 3TA-, PEG-, and DMSA-coated Fe 3 O 4 nanoparticles are well dispersed in aqueous solution. The average particle sizes of the Fe 3 O 4 and the 3TA-, PEG-, and DMSA-coated magnetite nanoparticles were exhibited approximately 10.4, 12, 11, and 12 nm by TEM results. The mean blocking temperatures of the uncoated Fe 3 O 4 and the 3TA, PEG, DMSA surface-coated Fe 3 O 4 nanoparticles exhibited about 245±10 K, 220±10 K, 142±12 K, and 200±10 K, respectively. The values of g factor of the uncoated Fe 3 O 4 and the 3TA-, PEG-, and DMSA-coated Fe 3 O 4 nanoparticles were obtained 2.22, 2.21, 2.22, and 2.19, respectively.