This dataset containing the synthesis methods, phase and particle size of iron oxide nanomaterials have been collected from previously reported studies as well as experimental data collected in the laboratory at Pacific Northwest National Laboratory, USA. The dataset includes 780 pieces of data corresponding to iron oxides synthesis in different sets of conditions, including precursors, additives, solvents, concentrations of each ingredient and temperature. The corresponding phases of the iron oxides such as hematite (a-Fe2O3), maghemite (g-Fe2O3), magnetite (Fe3O4). Goethite (α-FeOOH), akageneite (β-FeOOH), lepidocrocite (g-FeOOH), ferrihydrite and the size of the nanoparticles were also included in the dataset. The dataset was consisted of about 729 sets of data from previous publications reporting the iron oxides synthesis from 2010 to 2020 as well as the 51 sets of laboratory experimental data.