In this study, we have attempted to synthesize Fe3O4 nanoparticles by the thermal decomposition method without using toxic organic surfactants and solvents. Poly(ethylene glycol), PEO was being used as both solvent and surfactant simultaneously to synthesize Fe3O4 nanoparticles of controllable particle size and narrow size distribution. PEO has been widely used as a green solvent for various organic syntheses due to its low toxicity and high boiling point.