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There is a growing interest in using subsurface flow constructed wetlands as a method for treating domestic wastewater. More information about wetland sizing and the effects of plants on wastewater treatment is needed to improve the design criteria. Four wetland cells were constructed, and the hydraulic and organic loads of domestic wastewater were varied. To investigate sizing, the wastewater depth in cells were varied. Water quality parameters were measured for different depths. A comparison of planted vs. unplanted wetland cells was also conducted. Results showed that increasing the depth in the wetland did not significantly increase reduction of biological oxygen demand (BOD), even though detention time was increased. The BODs for effluent wastewater were consistently 18 to 22 mg L -1 better than those predicted by the EPA design equation when hydraulic loads were greater than 1.0 m 3 d -1 . Findings showed that under the same organic loads the cell containing plants reduced influent wastewater BOD values to 13 mg L -1 , while the cell without plants reduced influent wastewater BOD values to 21 mg L -1 . Planted cells also reduced influent NH4 + values 35% more and fecal coliform numbers by 30% more than unplanted cells. Our study suggests that subsurface flow constructed wetlands can effectively treat domestic wastewater.