In this study, a novel chitosan‐based nanoadsorbent has been synthesized by the reaction between nanochitosan and epoxy‐triazinetrione. The commercial cationic dye, malachite green, was chosen as a model dye in order to inspect the adsorption efficiency of the prepared adsorbent. The kinetics and thermodynamics of the adsorption process have been explored. According to the results, the Freundlich isotherm and pseudo‐second‐order model can well elucidate the adsorption process. The obtained thermodynamic parameters indicated that the removal process was spontaneous and endothermic (ΔH° = 95.0 kJ mol−1). The effects of several parameters on the dye elimination were studied using the response surface methodology approach. A high adsorption efficiency (95%) was obtained at 29.5 min, pH 7.9, and 7.5 mg of the adsorbent. At this condition, the removal efficiency of the unmodified adsorbent was 65.4%. The novel epoxy‐triazinetrione‐modified chitosan nanosorbent was found to be highly adequate for the treatment of wastewaters containing organic dyes.