A special place in the history of interstate relations between Indonesia and Malaysia is occupied by the territorial issue, which to a certain extent is complicating the strengthening of bilateral ties between friendly countries. The article is devoted to the problem of delimitation of the Indonesian-Malaysian border in Ambalat block, which is located in the Sulawesi Sea. Special attention is given to the process of formation and transformation of this issue in the historical perspective, its legal and technical aspects. On the basis of the studied materials, an attempt is made to identify the prospects for development and possible solutions to the problem under consideration.