Battle of the Japan Sea (Japanese: 日本海大海戦, Hepburn: Nihonkai Daikaisen, lit. 'The Great Battle in the Japan Sea') is a 1969 Japanese epic war film directed by Seiji Maruyama, with special effects by Eiji Tsuburaya. The film stars Toshiro Mifune, Yūzō Kayama, Tatsuya Nakadai, Toshio Kurosawa, Makoto Satō, Ryutaro Tatsumi, Chishū Ryū, and Matsumoto Kōshirō VIII. In the film, the Imperial Japanese Navy and army fail in their attempts to seize Port Arthur, and the Russian Pacific Fleet bears down on the Japan Sea during the Russo-Japanese War.

Battle of the Japan Sea was the last film for Eiji Tsuburaya before his death. A dedicated team of 60 artists worked on the 107 miniature ships created for the film. In addition, the miniature of the battleship Mikasa was made up to 13 meters long. Due to the weaker shell power during the Russo-Japanese War in the Pacific War, Freon gas was used to represent the water column in the naval battle scene.

The film was theatrically released in Japan by Toho on August 1, 1969 and earned ¥360 million, against a production budget of ¥350 million, during its theatrical run, making it the second-highest-grossing Japanese film of 1969.