Different quantities of silicon and calcium were added to Mg–6%Zn–1%Mn alloy and its effect on corrosion behavior investigated. AC and DC polarization were carried out on the extruded rods, which contain different quantities of silicon and calcium. The phases present in the alloys have been identified by optical microscopy and TEM. Four different phases were found, i.e., intermetallics containing Si–Mn, Mg–Si, Mg–Zn, and Mg–Si–Ca phase. The corrosion behavior of the studied alloys were influenced by the amount and distribution of the second phases.