After graduating from high school she turned professional and signed a contract with Nike Japan. In the 1983 season she won her first 400 m title at the Japan Championships, but relinquished her 200 m title to Emiko Konishi. She regained her 200 m title in 1984 and was not defeated nationally in the event for another four years. Her win streak of five only came to an end in 1989 when Toshie Kitada took the crown. She was a prominent pick for the 1985 Asian Athletics Championships but was less successful that year. She placed last in eighth in the 200 m final, could only help the Japanese women to sixth in the 4×100 m relay, but did manage to come away with a silver in the 4×400 m relay, behind a P. T. Usha-led Indian team. In November that year she helped set an Asian record in the infrequently competed 4×200 metres relay. The team of Konishi, Etsuko Hara, Isozaki and Koshimoto ran a time of 1:35.90 minutes in Hamamatsu. This record stood for nearly thirty years, with a Chinese team finally beating it at the 2015 IAAF World Relays.