Although there is a story that Mikizo OISHI was killed in a sword fight with a Shinsengumi member Yujiro IMAI,, according to the correspondence of Isami KONDO and Toshizo HIJIKATA., he died of illness.
新選組隊士・今井祐次郎に斬殺された話が伝わるが、近藤勇・土方歳三書簡によると病死。