The emergy methodology was used to evaluate aggregate supply from marine sand extraction at an offshore site in the exclusive economic zone in the South Sea of Korea for use in the construction of the Pusan New Port. The marine sand from the offshore site had an emergy yield of 2.87 E22 sej, with 97.5% from the offshore sediments and 2.5% from the economy. The emergy yield ratio of the marine sand extraction was 40.7, implying that the process contributed a net benefit to the Korean society beyond the economic inputs required for it. The environmental loading ratio of the sand production was, however, very high at 3,422, indicating the great environmental stress of the extraction process to the marine ecosystem. The emergy sustainability index, therefore, was very low at 0.012. This study revealed that the marine sand extraction could be a viable option in terms of yield, but measures to reduce environmental impacts of the extraction are needed to increase the sustainability of the process. Further emergy evaluations on other aggregate production alternatives are required to provide better insight in determining policy priorities regarding the aggregate supply for the construction sector of Korea.