Biosynthesis of nanoparticles has become a great interest in recent times due to their environmental friendliness and capability for preparing metallic, oxides, and also magnetic nanoparticles. This research studies the biosynthesis of ferric oxide nanoparticles using Pometia pinnata J.R.Frost. & G.Forst (Matoa) leaves water extract with a precursor of FeCl3.6H2O. The resulted nanoparticles can be directly observed from solution color, which changes from yellow to black after a chemical reaction occurred. Evaluation of the nanoparticles using permanent magnet showed that the agglomerated magnetic nanoparticles were attracted to the permanent magnetic disc. For the structure characterization, TEM, XRD and PSA instruments were used. The average crystallite size was found to be about 20 nm in a bigger amorphous part of the nanoparticles from TEM images. This was also confirmed by the spectra of X-ray diffraction. These results established ferric oxide nanoparticles which can be prepared using biosynthesis directly with mixing matoa leaves extract and FeCl3.6H2O solution.