Tensile tests of FeO were performed at 600-1200 degreesC under strain rates of 10(-3)-10(-5)s(-1). Deformation behavior of FeO scales at high temperatures were investigated. Test specimens of FeO scales were prepared by complete oxidation of 99.999% pure Fe before the tensile test, and gas atmospheres were adjusted throughout the tensile test to maintain the scale chemistry. Oxide scale of FeO deformed plastically above 700 degreesC; fracture elongation increased and tensile strength decreased as the temperature increases. Elongation of 160% was obtained at 1200 degreesC. Steady-state deformation, where the stress saturated, was recognized above 1000 degreesC. The test results of strain-rate dependence of stress during steady-state flow suggest that deformation of FeO scale above 1000 degreesC results from dynamic recovery associated with dislocation climb.