Agarose-coated Fe3O4/SiO2 magnetic nanoparticles (Fe3O4@SiO2@Agarose) modified with sodium dodecyl sulfate (SDS) were synthesized for adsorption/desorption of cationic drugs applications. For this purpose, magnetic nanoparticles (MNPs) of Fe3O4 were synthesized via a chemical precipitation method and the MNPs were homogeneously included into a silica shell using a modified Stober process. The surface of the core-shell Fe3O4@SiO2 nanoparticles was then modified with SDS and covered with an extra outer shell of agarose. The particles were characterized by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray analysis, Fourier transform infrared spectroscopy and vibrating-sample magnetometer, differential scanning calorimetry, dynamic light scattering and zeta potential measurements. The applicability of the synthesized nanocomposite for the adsorption/desorption of phenazopyridine (PHP) as a cationic drug model from aqueous solutions was investigated. The effects of different parameters on the adsorption efficiency of PHP such as volume of sample, amount of adsorbent, pH of solution, and contact time were optimized by a central composite design (response surface) method, and effect of volume and type of eluent and desorption time was studied by a one-at-a-time procedure. Under the optimized conditions, a capacity of 41mgg(-1) of PHP was obtained for the sorbent with an adsorption efficiency of 92.6% (+/- 1.5) for 6 replicates. The adsorption isotherms were also studied for the sorbent, and the Freundlich model was found to be more applicable than the Langmuir model in interpreting PHP adsorption on the nanocomposite.