The oxidation behavior of Fe-30%Ni-12.5%Co Invar alloy possessing low thermal expansion-high strength has been studied by exposing it in temperature ranges of 1000~1200 in an air atmosphere. The formed oxide scale consisted of two layers, an outer layer and an inner layer, and the oxidation mechanism showed uniform growth for all oxidation conditions. The growth rate of the scale had a parabolic relationship with oxidation time, and the estimated activation energy for the growth of the whole oxide layer was approximately 19.84 kcal/mol. The outer scale consisted of five oxide layers, whose outermost scale consisted of major phase CoFe 2 O 4 containing a particulate Fe 2 O 3 phase. The oxide scale of Fe-30%Ni-12.5%Co had different compositions and phases from the Fe-30%Ni alloy investigated in previous studies. Especially, when the alloy was exposed for a longer oxidation time and at a higher temperature, the volume fraction ratio of CoFe 2 O 4 to Fe 2 O 3 was found to increase.