Acidification damage in anode mortar is caused by anodic reactions occurring during impressed current cathodic protection (ICCP) and significantly affects the lifetimes of external anodes. Hydroxy-activated Mg/Al double oxide (HDMO) material was introduced to mitigate acidification damage by stabilizing the hydroxide content around the external anode mortar. The modified external anode was evaluated by electrochemical and microstructure techniques. The results indicated that HDMO slowed the oxidation of the external anode and increased the Ca(OH)2 content in the external anode chemistry. Therefore, HDMO can potentially be utilized for the design of external anode mortar for the ICCP process.