Rathmore Grammar School, normally referred to simply as "Rathmore", is a Catholic grammar school in Finaghy, Belfast, Northern Ireland. The current and second lay principal of the school is Arthur Donnelly, who succeeded Thérèse Hamilton as principal at the beginning of the academic year 2021/22. Rathmore is one of the highest-performing and most competitive schools in Northern Ireland.

A grammar school is one of several different types of school in the history of education in the United Kingdom and other English-speaking countries, originally a school teaching Latin, but more recently an academically oriented secondary school.