The adsorption characteristics of crystal violet (CY)-modified amberlite IRA-120 resin for the removal of Co(II) ion from aqueous medium at different experimental conditions were established by means of batch method. The adsorption uptake was increased with the increase in contact time and temperature. The adsorption process was controlled by pseudo-first-order kinetic model. Adsorption isotherms were expressed by Langmuir and Freundlich adsorption models. The Freundlich adsorption model fitted the experimental data reasonably well compared to the Langmuir model. A well-known thermodynamic equation was used to assess the ΔG 0 (standard free energy change), ∆H 0 (enthalpy change), and ∆S 0 (entropy change). The thermodynamic data was indicative of the spontaneous nature of the endothermic sorption process of Co(II) ion onto CY-modified amberlite IRA-120 resin.