Jiro Oba participated in the Sino-Japanese War (1894-1895) and studied in Germany for five years. He was appointed an instructor at the Army Staff College. In the Russo-Japanese War (1904-1905) he was Vice Chief of Staff of the Third Army and took part in the capture of Port Arthur.
He was subsequently appointed Commander of theThird Division and then Commander of the Garrison Forces in Korea. Promoted to full general (1920). He was Inspector General of Military Education.