The emergy concept was used to valuate the contributions of a tidal flat ecosystem included in the fourth stage reclamation plan for the Youngsan River area to the Korean economy. Emergy contributions of the ecosystem were compared with those of economic valuations performed on the same ecosystem. The tidal flat ecosystem contributed 3.55 million Em\/ha annually. This, however, cannot be compared directly with those of the economic valuations because both methodologies approach the valuation of ecosystems in different perspectives. The emergy methodology is a donor-based valuation in which what goes into making a product or service is measured, while the economic valuation is a receiver-based approach in which human receivers determine the value of an ecosystem product or service. An emergy valuation was conducted for the three ecosystem functions included in the economic valuations to compare the results of both methodologies on the same basis. Fishery production and pollutants removal contributed 9.86 million Em\/ha/yr and 0.88 million Em\/ha/yr, respective1y. The conservation value of the tidal flat ecosystem was 3.55 million Em\/ha/yr. Overall, the emergy valuation that try to include works of both human and nature on the same basis resulted in higher economic contribution of the tidal flat ecosystem than that calculated by the economic methodologies in which only human works are measured based on the willingness-to-pay of people. This study showed that the emergy concept could provide an alternative tool for policy decision-making regarding utilization and conservation of ecosystems by approaching the ecosystem valuation from a different perspective than that of economic methodologies.