Racemic tris-oxalatocobaltate (III) complex ions were optically resolved by an optical active complex, ${Delta}$-tris-ethylenediamine cobalt (III), and then racemization of ${igwedge}-[Co(ox)_3]^{3-}$ obtained was investigated in various mixed solvent such as water-organic solvent (organic solvents=ethanol, iso-propyl alcohol, acetone, and dioxane). The rate of racemization was increased with following order; water < ethanol < acetone < isopropyl alcohol < dioxane; which is the same order for polarizability of organic solvent added. Considering ${Delta}H^{ eq},;{Delta}S^{ eq}$ and above facts for the racemization of ${igwedge}-[Co(ox)_3]^{3-}$, it seems to be twist mechanism of plausible mechanisms.