Magnetic Fe3O4 nanoparticles were synthesized by the co-precipitation method and modified with three different silane compounds (3-(trimethoxysilyl)propyl methacrylate, MPTMS; 3-(triethoxysilyl)propyl methacrylate, MPTES and triethoxyvinylsilane, VS). The nanoparticles were analyzed by FTIR, TEM, XRD, SEM-EDS, TGA and VSM. In addition, contact angle measurements were performed to determine the modification efficiency of silanes. The average particle size of Fe3O4 nanoparticles was found as 8.8 +/- 1.8 nm. The results showed that the structure of Fe3O4 nanoparticles were not affected by the surface modification. The most effective modification was obtained by VS with 7.8 +/- 1.0 nm average particle size and 83% (<= 10 nm) particle size distribution. VSM curves showed that Fe3O4 and also surface modified nanoparticles exhibited superparamagnetic behaviour. (C) 2014 Elsevier B.V. All rights reserved.