Abstract: The potential of removing steroids in raw domestic wastewater with various mesocosm-scale horizontal subsurface-flow constructed wetlands (CWs) with different design parameters is assessed. Twelve CWs with three hydraulic loading rates (HLR=10, 20, 30 cm/d) and four substrates (oyster shell, zeolite, medical stone and ceramic) were set up outdoors in order to obtain the optimum design parameters of CWs. Meanwhile, the pollutant removal mechanism with CWs was deduced with the mass balance analysis. The result showed that 9 target steroids including 4-androstene-3, 17-dione, 17α-boldenone, 17β-boldenone, androsta-1, 4-diene-3, 17-dione, androsterone, hydroxyprogesterone, medroxyprogesterone, medroxyprogesterone and testosterone were detected in the effluent. The concentrations ranged from 6.32 to 1 113 ng/L. The CWs with different design parameters had variable removals of conventional pollutants and steroids. The total removal rate of all detected steroids was between 27.7% and 94.9%. The calculated daily mass removals of COD, TN, NH₄⁺-N and steroids with the twelve CWs were 3.81~10.10, 0.42~1.07, 0.31~0.80 g/d, and 14.16~28.65 μg/d. Considering their aqueous removal rates in combination with their mass removals, the CW with zeolite as the substrate and with HLR of 20 cm/d was selected as the best. The results indicated that both biodegradation and substrate adsorption were responsible for the fate of steroids in the wetlands, but biodegradation was the most important process in the removal of these pollutants.