Synthesis of iron oxide nanoparticles (Fe-O NPs) from iron(III)acetylacetonate solution by femtosecond laser irradiation is reported. Fe-O NPs and carbon are agglomerated in nhexane, while single-nanometer-sized dispersed Fe-O NPs are obtained in water. We propose that the choice of ligands and solvent determines the primary particle size distribution and dispersion states of NPs as well as carbon contaminants in laser-assisted synthesis using metal complexes as reactants.