A magnetic dye-adsorbent catalyst has been processed by subjecting the conventional magnetic photocatalyst to a hydrothermal process followed by typical washing and thermal treatments. It has been characterized using the transmission electron microscope, X-ray diffraction, X-ray photoelectron spectroscope, and Fourier transform infrared spectroscope for analyzing its morphology, structure, and surface chemistry. It consists of a composite particle having a "core-shell"structure, with a magnetic particle as a core and nanotubes of dye adsorbent as a shell. The dye-adsorption behavior of magnetic dye-adsorbent catalyst and the conventional magnetic photocatalyst has been measured, under the dark condition, using methylene blue (MB) as a model catalytic dye agent. It has been demonstrated that, due to its higher specific surface area, the magnetic dye-adsorbent catalyst removes an organic textile dye from an aqueous solution via surface adsorption mechanism, which is in contrast to the photocatalytic degradation mechanism, under the ultraviolet radiation exposure, associated with the conventional magnetic photocatalyst. It has been shown that, the magnetic dye-adsorbent catalyst removes >99% of MB dye from an aqueous solution in just 30 min via surface adsorption mechanism. The magnetic dye-adsorbent catalyst also possesses magnetic properties, which makes its removal from an aqueous solution possible using an external magnetic field after the dye-adsorption process.