Abstract: The polystyrene (PS) microspheres with a micro-mesoporous structure were synthesized by suspension copolymerization using maleic anhydride (MAH) as a comonomer, followed by a hyper-crosslinking reaction using dichloromethane as a crosslinking agent and anhydrous aluminum chloride as a catalyst. The resultant PS microspheres were further characterized to determine their chemical structure and morphology by specific surface area test, scanning electron microscopy, Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy. Moreover, the water absorption and pentobarbital adsorption performance of the microspheres were measured. The results indicated that the specific surface area of the microspheres was significantly improved by the hyper-crosslinking reaction. The water absorption and pentobarbitol adsorption performance were also enhanced with an increase of MAH content. The microspheres achieved a maximum pentobarbital adsorption capacity of 91.90 % at the MAH content of 20 wt%.