a b s t r a c tMesoporous silica such as MCM-41 was used as an adsorbent for the removal of cephalexin antibiotic from synthetic wastewater. In this study, MCM-41 adsorbent was synthesised and was characterised by FE-SEM, XRD, FTIR and isotherms of adsorption/desorption of N 2 . The effects of initial pH, adsorbent dose, initial adsorbate concentration, contact time and temperature on process efficiency were evaluated using Box-Behnken statistical experiment design (RSM). FTIR analysis revealed the Si-OH, H-O-H and Si-O-Si bonds are formed. According to BET surface area, MCM-41 had pores with a diameter of more than 2.0 nm and surface area of 1,097 m 2 g -1 and also XRD spectra showed the mean crystallite size of MCM-41 was 75 nm. The statistical results show that pH, adsorbent dose, initial antibiotic concentration, temperature and quadratic pH were significant and presented with probability <0.05. The optimum removal condition based on analysis of variance and the quadratic model was the initial pH of adsorbate solution fixed at 3.00, adsorbent dose 800 mg L -1 , the initial concentration of antibiotic at 50.0 mg L -1 , a temperature of 40.0°C, and at the adsorption time of 30.0 min. Under these conditions, the percentage removal of cephalexin antibiotic was 90.3%. Therefore, according to the obtained results, the mesoporous silica can be used to adsorb cephalexin antibiotic in optimal conditions designed by response surface methodology.