The partitioning of Mg²⁺, Fe²⁺ and Mn²⁺ ions between spinel group minerals (spinel and magnetite series minerals) and 1 molal aqueous chloride solution was experimentally investigated at 600°C and 1 kb using standard cold-seal type pressure vessels. The experiments were carried out for the following six binary systems; spinel-hercynite, hercynite-galaxite, galaxite-spinel, magnesioferrite-magnetite, magnetite-jacobsite and jacobsite-magnesioferrite. Continuous solid solutions were formed in all of the systems. The cations are preferentially partitioned into the spinel series minerals in the order of Mg²⁺>Fe²⁺>Mn²⁺, and into the magnetite series minerals in the order of Fe²⁺>Mg²⁺>Mn²⁺. The cation partitioning between spinel and magnetite series minerals was derived from the above experimental results, which indicates that the formers prefer Mg²⁺ but the latters Fe²⁺ and Mn²⁺.