A novel polysaccharide-based hydrogel nanocomposite was prepared using grafting of acrylic acid (AA) on to kappa-carrageenan (κC) by incorporating multi-walled carbon nanotube (MCNT). In fact, MCNTs were used as nano-sized reinforcements in the synthesized nanocomposite. Spectroscopy together with morphology proved relatively strong κC-MCNT interaction. Besides, the swelling behavior of the nanocomposite hydrogel was studied. The results showed that in the presence of MCNTs, the equilibrium swelling capacity was decreased. This can be attributed to cross-linking role and hydrophilicity nature of MCNTs. The adsorption performance of hydrogel nanocomposite was also investigated for the removal of crystal violet (CV) as a cationic dye. The effects of some important parameters such as MCNT concentration, pH and contact time on the uptake of CV solution were studied. Equilibrium adsorption isotherm data of the hydrogel exhibited better fit to the Langmuir than to the Freundlich isotherm model. According to this model, the maximum adsorption capacity of κC-based hydrogel nanocomposite was found to be 118 mg . g-1.