The goal of this study was to prepare nanocomposites of rice straw coated with different percentages of Fe 3 O 4 nanoparticles (Fe 3 O 4 -NPs) [1.0, 5.0, 10.0, and 20.0 wt. %]. In this process, the size of Fe 3 O 4 -NPs changed with varying volumes of NaOH (2M). The Fe 3 O 4 -NPs were precipitated with sodium hydroxide from a solution of Fe(II) and (III) chloride in water under ambient conditions and N 2 gas by the quick precipitation method using urea as a stabilizer. The rice straw/Fe 3 O 4 nanocomposites (NCs) prepared by this method had magnetic properties in percentages higher than ten (10 wt. %). When the volume of NaOH increased, Fe 3 O 4 -NPs with uniform size and better distribution could be prepared, which means that the size of the NPs decreased as the reducing agent was increased. Transmission electron microscopy (TEM) showed that Fe 3 O 4 -NPs in rice straw were spherical with diameters from 18.47 to 9.93 nm. The SEM results show that the structure of rice straw underwent no particular change. EDX indicated the presence of Fe 3 O 4 -NPs on the surface of rice straw. X-ray powder diffraction (PXRD) indicated that the magnetic Fe 3 O 4 -NPs were pure and that the particles were small. The FT-IR results showed that the Fe 3 O 4 -NPs were successfully coated on the surface of rice straw.