The 1977–78 season was the 63rd season of the Isthmian League, an English football competition. At the end of the previous season league divisions were renamed: Division One was renamed the Premier Division and Division Two was renamed Division One. Also, seventeen new clubs were newly admitted to the league, they were placed to the new Division Two, as the league expanded to three divisions. Enfield won Premier Division, whilst Dulwich Hamlet won Division One and Epsom & Ewell won Division Two.