The 1979 Japan Open Tennis Championships, also known by its sponsorship name Hit-Union Japan Open Tennis Championships, was a combined men's and women's tennis tournament played on outdoor clay courts in Tokyo, Japan that was part of the Colgate Series and the Volvo Grand Prix circuit. The tournament was held from 22 October through 28 October 1979. Terry Moor (ninth-seeded) and Betsy Nagelsen won the singles titles.