[1] Mizuhara played his entire professional career for the Tokyo Giants/Tokyo Kyojin/Yomiuri Giants, from the Japanese Baseball League's beginnings in 1936 until 1950.

Playing second base for Tokyo in 1942, Mizuhara was voted Most Valuable Player of the JBL.

[2] The JBL reorganized to Nippon Professional Baseball in 1950, and Mizhuara became player-manager of the Giants (although he retired as a player after the season).

As manager for the Giants from 1950 to 1960, the Toei Flyers from 1961 to 1967, and the Chunichi Dragons from 1969 to 1971, Mizuhara compiled a record of 1586–1123, for a .585 winning percentage.

As manager, he guided his teams to five Japan Series championships, four of those with Yomiuri and one with Toei.