Administrative mergers of cities have increased since the 1960s, aiming at area development with the progress of industrialization and urbanization in Japan. As a result of these mergers, many new cities have more than two centrall built-up areas. This has given rise to several topics of debate, including: distribution of government investment; formation of appropriate urban structures ; etc. It is there-fore necessary to study the changing urban structure of merged cities. The purpose of this paper is to clarify the spatial change in the urban structure of Joetsu city after a merger. The study area was incorporated by the merger of the two cities of the same scale, Takada and Naoetsu, in 1971. It had two separate built-up areas when the two cities merged. The transportation network has been rearranged and the built-up areas have expanded in the past 25 years. The ur-ban structure of Joetsu city has changed accordingly. The paper focuses on three aspects: first, the relation between the process of the merger and the city planning of the new city; second, the functions of city planning and the location of main public facilities; and third, the formation of new built-up areas between two previously existing built-up areas. The results obtained are summarized as follows: (1) Takada and Naoetsu, each of which had a central built-up area, merged on equal terms. This merger affected the urban planning of Joetsu city. To establish a new city, the local government had to redevelop the two existing built-up areas at the same time or build a new administrative center between the built-up areas of Takada and Naoetsu. Joetsu city adopted the latter plan. (2) The local government used city planning which aimed at urbanization between the built-up areas of Takada and Naoetsu (Figs. 2, 3, 4, and 5), because the two cities merged on equal terms. In the early 1970s, new administrative and cultural facilities were constructed intensively in the Kida area around Kasugayama Station. Since the 1980s many public facilities have been constructed in the Sekikawa-East area, and large-scale retail stores have also located there. (3) Joetsu city now has new administrative and cultural centers in the Kida and Sekikawa-East areas, as well as the previously existing Takada and Naoetsu central built-up areas. The urban structure of Joetsu city has become more dispersed due to the equal merger of two cities.