In 1925, finding formal theological study to be inherently unfulfilling, Sergei left the Institute and Paris to become a monk on [[Mount Athos]].

Sergei arrived at Mt Athos in 1926, where he entered the [[St. Panteleimon's Monastery (Athos)|Russian Orthodox Monastery of St. Panteleimon]] with the intent of learning how to pray and to have the right attitude towards God. He was [[tonsure]]d with the name of Sophrony. In 1930, Fr Sophrony was ordained to the [[diaconate]] by St [[Nikolai Velimirovic|Nicolai (Velimirovic) of Zicha]], and he became a disciple of St [[Silouan the Athonite]], who would prove to be Fr Sophrony's greatest and life-long influence. St Silouan had no formal system of theology, being largely uneducated, but his life exuded theology. This is what taught Fr Sophrony, and what Fr Sophrony would later systematize.