J.R.R. Tolkien studied Classics at Oxford before changing direction toward English language and literature.
He entered Exeter College, Oxford, in 1911 and initially studied Classics. After his first examinations, Tolkien changed his course to English Language and Literature. His later academic interests in philology, Old English, Middle English, and historical linguistics became central to both his scholarship and his creative writing.
Tolkien’s early study of languages helped shape the invented tongues and naming systems of Middle-earth. He was particularly interested in how languages develop, change, and preserve traces of earlier cultures. That interest contributed to the depth of his fictional histories and peoples.
The answer is not “English,” even though English became his degree subject and professional field. The question asks what he studied before that change. Tolkien’s initial Oxford subject was Classics, which included the languages and literature of ancient Greece and Rome.