Mg alloys have unique characteristics such as high specific strength, low density, high corrosion rate, etc., as functional as well as structural materials. Mg-Zn alloys have good biocompatibility because Mg and Zn are abundant nutritional elements in the human's body. However, Mg alloys with multiphase cause galvanic corrosion by corrosion potential differences among constituent phases. Therefore, the application of Mg alloys on bio-material parts are limited. In this study, bio-corrosion properties of Mg-Zn-Mn alloys according to the solid solution and distribution of phases by various Mn contents and heat treatment condition were evaluated. The results of tensile and in-vitro corrosion tests indicated that tensile and bio-corrosion properties could be adjusted by controlling the Mn contents and heat treatment. The tensile yield strength (TYS), ultimate tensile strength (UTS) and Elongation of Mg-Zn-Mn alloys increased up to 0.5 wt.% and then slightly decreased with Mn contents. However, TYS, UTS, and Elongation of T4 treated Mg-Zn-Mn alloys increased with increasing Mn contents. When MgZn phase and Mn particle were dissolved in the matrix, bio-corrosion properties were improved in hank's solution. From the results of immersion test, the Mg-3Zn- 0.5Mn alloy has good corrosion properties at 2 steps T4 treatment.