Cesium (Cs) is a major product of uranium fission, which is one of the most existed radionuclides in radioactive wastes. Removal of Cs-137 has a critical role in the decontamination of liquid radioactive waste due to its halflife of 30.17 years. Concordantly, melamine styrene based conjugated polymer (MSP) was designed, synthesized, and characterized with FTIR, TGA, SEM and BET measurements. The novelty of the study is that the MSP adsorbent is designed as a highly conjugated structure to have better interaction with Cs over the Cs-pi bond of the benzene groups of the adsorbent. In this work, the adsorption behavior and rate of MSP were investigated as parameters of adsorbent amount, pH, contact time, particle size, initial Cs+ concentration, and temperature. Besides, the adsorption efficiency of Cs-137 was examined by Gamma Spectroscopy. Adsorption results were fitted to three different isotherms which were Freundlich, Langmuir and Dubinin-Radushkevich (D-R). The maximum adsorption capacity of polymer for Cs+ ion was found from Langmuir isotherm as 78 mg g(-1). As a part of kinetic parameters, pseudo first and second orders were investigated and in terms of the correlation coefficient pseudo second order was much more appropriate for adsorption of Cs-137 onto MSP.