Poly(styrene)/poly(styrene-co-methacrylic acid), PSt/P(St-co-MAA), core-shell microspheres were synthesized through a facile emulsion polymerization method, and the synthesized particles were alkali treated to creat a rough surfaces microspheres. The microspheres effectively served as a highly efficient adsorbent for eliminating the cationic dye methylene blue (MB) from water. The diameter of the particles was measured, and the various techniques including FT-IR, SEM, TGA were employed to characterize the prepared PSt/P(St-co-MAA) microspheres and the MB-adsorbed microspheres, PSt/P(St-co-MAA)-MB. The influence of various factors, including initial pH, dye concentration, dyeing bath temperature and contact time on the dye adsorption capacity was thoroughly examined using the batch-adsorption method. The adsorption capacity progressively increased as the pH of the dyeing bath, dye concentration, temperature, and contact time were raised. The findings revealed that the adsorption capacity could reach as high as 198.7 mg g-1 at 25 °C. Additionally, the adsorption kinetics suggested that the adsorption process followed the kinetic model of pseudo-second-order. The equilibrium adsorption data were well-represented by the Langmuir isotherm model. Thermodynamic analysis indicated that the adsorption process was endothermic, spontaneous, and classified as physisorption. The findings demonstrate that the PSt/P(St-co-MAA) microspheres are highly effective for the removal of cationic dyes from wastewater.