The first results of high-speed atomic oxygen (AO) irradiation tests for atomically thin single-layer graphene sheets are presented as space environmental tolerance evaluation tests toward application in astronomy. The single-layer graphene sample was prepared without a metal coating, and high-speed AO irradiation tests were conducted with an averaged velocity of ∼6 km/s using a laser-detonation AO beam source assuming a low Earth orbit (LEO) case. The Raman spectral features were examined before and after the tests with fluence values of 2×1015, 2×1016, 2×1017, 2×1018, and 2×1019 atoms/cm2. It was found that there is no significant change in the observed D/G ratios for fluence up to 2×1017 atoms/cm2. In contrast, the D/G ratios changed from 0.04±0.03 to 0.8±0.4 for 2×1018 atoms/cm2 drastically in both the averaged value and 1-sigma range. Furthermore, the D/G ratio could not be measured beyond 2×1019atoms/cm2 because no peaks were observed in both the G and D bands, which suggests that the degradation occurs between 2×1017 and 2×1018 atoms/cm2 and no graphene sheets exist after the 2×1019 atoms/cm2 irradiation. Scanning electron microscopy images also support this conclusion in terms of the observed image contrast. Consequently, to protect the single-layer graphene sheets from erosion, a special treatment such as coating is needed to survive in an LEO for ≳ a day.