A burner stabilized premixed low-pressure flame has been used to generate iron-oxide (Fe2O3) nanoparticles with sizes in the range 7–20 nm. The H2/O2/Ar flames were doped with different amounts of iron-pentacarbonyl (Fe(CO)5) with concentrations in the range 524–2096 ppm. The influence of precursor concentration on composition, structure, morphology, and size have been studied utilizing transmission electron microscopy (TEM), X-ray powder diffraction (XRD), measurements of the specific surface area (BET), and infrared spectroscopy (FT-IR). The product particles consist of both, the γ- and the α-phase of Fe2O3. Average particle sizes were measured in the range 7.4–16 nm depending on precursor concentration and flame conditions.