A 4.5μm-thick Cr film prepared by a double glow sputtering technique was deposited on a magnetic Sm(Co bal Fe 0.22 Cu 0.08 Zr 0.02 ) 7.5 alloy to improve its oxidation resistance. Oxidation tests in air at 700°C indicate that the Cr film grew a Cr 2 O 3 scale, profoundly preventing the oxidation of the SmCo-based alloy. The coated alloy only formed a ∼2.9μm-thick internal-oxidation-affected zone (IOAZ) for 20h. The mechanism for the formation of this IOAZ, together with its induced alloy magnetic phase transformation, is presented.