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A facile and simple approach for the synthesis of nanosized iron oxide and oxyhydroxide using biogenic polyamines is described. At room temperature, the highly crystalline nanoparticles of magnetite (Fe304) with average sixes of 44 ± 2 and 37 ± I nrn were synthesized with spermine and spermidine, respectively. The magnetite nanoparticles formed by the biogenic polyamines exhibited a ferrimagnetic behavior at room temperature. When the same reaction was carried out at low temperature, crystalline nanorods of lepidocrocite (γ-FeOOH) with a high aspect ratio were formed. It was revealed that the lepidocrocite nanorods with an aspect ratio of 70 formed bundles, each of which consisted of several nanorods stacked together by the side on fashion. It was suggested that the nanorods are of single-crystalline nature and exhibit a superparamagnetic behavior at room temperature. As the reaction temperature increased from 40 to 70°C, the formation of magnetite nanotetrapods, nanorods, and nanoparticles was observed depending on the reaction temperatures. Magnetic properties of products were demonstrated to depend on the morphology, the degree of crystallinity, and the presence of amorphous oxyhydroxide. [ABSTRACT FROM AUTHOR]