The 1977–78 OMJHL season was the fourth season of the Ontario Major Junior Hockey League (OMJHL). The Fincups franchise moved back from St. Catharines to Hamilton after a temporary year away from the city due to lack of a suitable arena. The league featured a wealth of scoring talent during the season, with two players recording the league's highest single season point totals. Third season veteran Bobby Smith, edged 17-year-old rookie Wayne Gretzky for the Eddie Powers Memorial Trophy, scoring 192 points; as of 2023, Smith's and Gretzky's performance this season still stand as the top two scoring totals in OHL history. Twelve teams each played 68 games. The Peterborough Petes won the J. Ross Robertson Cup, defeating the Hamilton Fincups.

The Peterborough Petes are a junior ice hockey team in the Ontario Hockey League. The team has played at the Peterborough Memorial Centre in Peterborough, Ontario, Canada, since 1956, and is the oldest continuously operating team in the league.