The corrosion behavior of four Mg–5Al–xCa alloys (x = 0.0 to 2.0 wt.%) was evaluated in an alkaline NaCl solution. Surface analyses indicated that the benefits of Ca addition are the refinement of the precipitates and a decrease in grain size. Furthermore, the refinement of the precipitates (Mg 2 Ca, Al 2 Ca) became more complete with increasing of Ca content. The electrochemical tests revealed that the pitting resistance was improved in Ca-containing specimens. In addition, the polarization resistance of the Mg–5Al specimens increased with increasing Ca content. This is due to the fact that precipitation which is expected to act as a barrier is more continuous over the Mg matrix with a smaller grain size and higher precipitation density.