This study involved the utilization of a free radical-graft copolymerization reaction for the development of a novel adsorbent, namely, poly(butyl methacrylate)grafted alginate/Fe 3 O 4 nanocomposite (PBMA-gft-Alg/Fe 3 O 4). Transmission electron microscopy, scanning electron microscopy, energy-dispersive X-ray analysis, X-ray diffraction patterns analysis, and Fourier transform infrared spectroscopy (FT-IR) were carried out for the characterization of Fe 3 O 4 NPs and PBMA-gft-Alg/Fe 3 O 4 nanocomposites. The capability of nanocomposites and nanoparticles to adsorb dyes such as MG and MB, resulting in their removal from aqueous media, was evaluated under different conditions such as pH, temperature, contact time, and dose of adsorbent. Optimum parameters for adsorption of dyes were found to be pH of 10, 50 C, contact time of 180 min, and 0.2 g of adsorbent. Efficiency of the PBMA-gft-Alg/Fe 3 O 4 nanocomposite was found to be significantly greater than that of Fe 3 O 4 NPs for eliminating the desired dye. Langmuir, Freundlich, Sips, and Temkin models were used for testing the experimental data. Freundlich model was the one that best described the adsorption.