This study focuses on the influence of solution heat treatment 011 mechanical properties and corrosion by immersion of extruded Mg5Gd. The results are compared to pure Mg. Since Mg5Gd could be considered as a biodegradable magnesium alloy. Ringer solution has been chosen for corrosion tests. Hardness and tension tests reveal a loss in strength by solution heat treatment resulting from strong grain growth and dissolved second phases. The addition of the alloying element Gd improves the corrosion behavior, the amount of corrosion pits is reduced. The pure Mg extrusion bars in comparison have a higher corrosion rate and show strong pitting. The corrosion morphology is described by the pitting factor. Even there is less microgalvanic coupling because of dissolved second phases, solution heat treatment does not improve the corrosion rate of Mg5Gd by a great amount, making the strong grain growth responsible for that. However, Mg5Gd-T4 shows highest pitting corrosion resistivity.