The Battle of Bonari Pass (Japanese:母成峠の戦い) was part of the Boshin War, and occurred on the 6 October 1868 (Gregorian Calendar), or the 21st day of the Eighth Month, Keiō-4 year (Japanese calendar). The Bonari pass was a strategic access at the limit of the fief of Aizu. Three days later, the Imperial troops reached the castle of Wakamatsu and led siege to it, in the key action of the Battle of Aizu.