Fe3O4 nanoparticles (NPs) have been synthesized by the thermal decomposition of iron oleate complex in 1-octadecene solutions using organic amines as stabilizers such as trioctylamine (TOA), oleylamine (OAm), and hexadecylamine (HDA). By optimizing preparation conditions such as temperature, time, and the concentration of reaction reagents, the NPs exhibited adjusted sizes and morphologies (spherical, truncated octahedral, cubic, and tetrahedral). Organic amines play an important role for the morphology of the NPs. For example, truncated octahedral-shape was gradually changed into quasi-cubic shape if adding TOA in the reaction system for a long time. In contrast, spherical, cubic, and tetrahedral Fe3O4 NPs were fabricated in the case of OAm used. Because of OAm used as a reducing agent, reaction temperature was decreased. HDA resulted in spherical Fe3O4 NPs a large size. It is confirmed that organic amine molecules were bound on the surface of the NPs by measuring the Fourier transformation infrared spectroscopy of samples. (C) 2013 Elsevier Ltd. All rights reserved.