Constructed Wetlands are used in many parts of the world for the treatment of wastewater from diverse sources. They are effective, low cost and sustainable alternative to most conventional wastewater treatment processes. They are engineered to mimic many of the same processes that occur in natural wetlands but within a more controlled environment. The need for proper design of constructed wetlands for secondary and tertiary wastewater treatment is of utmost importance in meeting today's stringent water quality standards. Subsequently, numerous design tools have been proposed for the assessment of constructed wetland performance. Currently, applied modeling approaches include regression models, mass loading versus outflow concentration analysis, Monod type analytical models and first-order removal kinetic models. The principal objective of this research was to estimate the biochemical oxygen demand (BOD) removal using both the plug flow and complete-mix first order kinetic models. Results obtained by these models were then validated by comparing with published data from the Arcata constructed wetland. This study also investigated the sensitivity of effluent BOD quality to variation in influent concentration, temperature and hydraulic retention time. Analysis of the results revealed that variations in the field conditions influenced the removal rate of BOD in each zone of the wetland. The design reaction rate coefficient for each zone varied and was corrected for using the Arrhenius expression. The BOD removal performance of the Arcata wetland and any wetland operated under similar conditions was found to be better modeled by the plug flow model at zero background concentration. The study also found the BOD removal to be much influenced by the influent concentration and minimally influenced by temperature and hydraulic retention time.