Hydrogen isotope concentrations in erbium oxide coatings fabricated by filtered arc deposition and metalorganic decomposition have been investigated using nuclear reaction analysis and secondary ion mass spectroscopy. It was found that deuterium concentration in the coatings fabricated by filtered arc deposition was 300-500 atomic parts per million, whereas the deuterium concentration in the coating fabricated by metal-organic decomposition was approximately 2.0 × 10 4 atomic parts per million due to hydrogen trapping by carbon impurities. Deuterium concentrations in the coatings by filtered arc deposition increased with increasing depth in accordance with the increase of grain boundary area density. An in-plane deuterium distribution of the coating by secondary ion mass spectroscopy proved the segregation with a net-like structure, indicating that the deuterium diffused through the grain boundaries.