Population and the environment are the basic elements of a human ecological system having intrinsic links between them. But, research on their relationships is very limited in both quantity and depth. Although the concern on the topic has grown recently, most discussions lack analytical perspectives and are largely descriptive. The tendency is blamed for problems involved in defining the term, the environment, and the paucity of data on environment. In Korea, the limitation is much grater and, therefore, this study sets a moderate aim: That is, to explore, from ecological perspectives, various implications of population change on the environment in 20th century Korea. More specifically, it examines the related theoretical discussions, the major features of population change, and changes in environmental conditions that can be assumed to have direct or indirect links with population size and urbanization. Official statistics and newspaper articles on various environmental issues consist of the major data sources.