Although construction of wetlands to improve water quality has been increasing recently, the functional development of the constructed wetland has not been thoroughly investigated. The soil in a wetland can be a good indicator for assessing the capability of a wetland to improve water quality.The soil has a profound effect on the growth of wetland plants as well as the retention of nutrients and contaminants. In this study, the changes in the microbial activity and physicochemical properties of a wetland soil after wetland construction was assessed. Changes were quantified for the following parameters; dehydrogenase activity (DHA), denitrification potential (DNP), soil texture, water content, pH, CEC(cation exchange capacity), organic matter content, total nitrogen, and available phosphorus. There parameters were monitored to investigate the effects of inundation and accumulation of organic matter and nutrients in the wetlands. Changes in soil and microbial properties of two constructed wetlands  with different contaminant inflow characteristics were compared to a natural wetland (reference wetland). There was a clear difference in soil texture between the natural and constructed wetlands with high sand content in the constructed wetlands and high clay content in the natural wetland. The soil of the natural wetland had a higher in water content and more organic matter but lower in pH than the constructed wetlands. CEC and nutrient concentrations of the constructed wetlands seemed to be affected mainly by inflows of organic matter and contaminants. The results showed that the DHA and DNP of the natural wetland soil were higher than those of constructed wetlands. The results imply that newly constructed wetlands required a period of time to improve contaminant removal performance through biogeochemical processes. Therefore, microbial activity levels and related physicochemical indicators should be considered during wetland management.