The effect of acid treatment on the high-temperature oxidation behavior of Fe-Cr-Al alloy has been examined with oxidation tests and various characterization techniques. Acid treatment effectively improves the stability of the alloy in a high-temperature oxidation environment. After the treatment, the alloy oxidizes at a higher rate in the induction period and a lower rate in the subsequent time period. A passivative oxide layer was determined to be better formed during high-temperature oxidation on the surface of the acid-treated alloy, which suppressed further oxidation. It was observed that the oxidation rate of the alloy at high temperature can be described precisely by the Quadakkers equation.