Laboratory erosion tests were conducted for preoxidized T2 steels in N2 gas atmosphere at 500°C for 30 min. Angular quartz particles of three different sizes of 49, 201 and 460 (μm were used as the erodent material. The total weight and velocity of the erodent quartz particles were varied. Generally, appreciable thickness loss was measured for the preoxidized specimens of higher erodent velocity and greater particle weight. On the other hand, no apparent thickness loss was found for specimens of lower erodent velocity and lesser particle weight. The effect of erodent particle size on the critical boundary of the occurrence of the thickness losses was not clear. For the test specimens of appreciable thickness losses, oxide scale was mostly detached and removed from the specimen surface probably through brittle fracture of the oxide scale upon continuous impingement of the quartz particles. For test specimens of no measurable thickness loss, the scale remained tenacious and protective during the erosion experiment. For these test specimens, thickness of the oxide scale did not change drastically and thinning of the oxide scale due to “erosion” was not observed. Conditions for the formation of cracks and flaws in the oxide scale by single erodent impingement of the quartz particle were investigated. For small particles of 49 μm, the critical particle velocity for the formation of cracks and flaws in the scale was between 10 and 15 m s−1, whereas that of 201 μm between 5 and 10 m s−1. For the large particle of 460 μm, indentation by a single erodent impact was noticed even for 5 ms−1. An erosion-corrosion mechanism of oxide scale formed on T2 steel by angular quartz particles was proposed and discussed based on the laboratory erosion test results obtained in this study.