The processes of vegetation development and interspecific association were studied as a part of a successional study in the sand bars at the Nagdong River estuary in Korea. The major pioneer plant species in the sand bars were Salsola komarovi, Carex pumila and Cynodon dactylon. In embryonic sand bars, Namusitdeung and Galmaegideung, the processes of vegetation development after colonization by pioneer species were closely interdependent with the development of the sand dune. The vegetation types of embryonic sand bars were divided into two groups: sand dune plants, and annual and perennial forbs. Those of old sand bars, Baeghapdeung and Ogryudeung, were also divided into two groups: sand dune plants, and salt marsh plants. The results of interspecific association concided well with the actual distribution of plant communities in the sand bars. The degree of vegetation development in each sand bar agreed with the order of successional stage observed in this study area.