Ōtori Keisuke (大鳥 圭介?, 14 April 1833 – 15 June 1911) was a Japanese military leader and diplomat.
Ōtori Keisuke was born in Akamatsu Village, in the Akō domain of Harima Province (modern-day Hyōgo), the son of physician Kobayashi Naosuke. At a young age, he entered the Shizutani school in Bizen, engaging in Chinese studies, and continued his education at the renowned Rangaku school of Ogata Kōan, where he studied Dutch language and medicine. Further learning was obtained in Edo, where Ōtori travelled to attend the school of Tsuboi Tadamasu, known for instructing students engaged in the study and translation of Dutch. While in Edo he also received education from Egawa Tarōzaemon regarding military strategy, and studied English with Nakahama Manjirō, thus coming into possession of an uncommonly thorough, for his era, appreciation of Western culture. As a result, in 1859, the Tokugawa Shogunate appointed him as an instructor to its Kaiseijo institute, and it was from there that Ōtori entered the Shogunate army.
After entering the Tokugawa army, Ōtori displayed promise as a student, quickly becoming a senior instructor of infantry tactics. After a period spent as a student of Jules Brunet in Yokohama, learning specifics of French infantry tactics, he was promoted to (Infantry Magistrate (歩兵奉行 Hohei bugyō?)), a rank equivalent to a four-star general in a modern Western army.