The thermally aged 10Cr-1Mo-1W-VNbN steels were charged with hydrogen by cathodic electrolysis and then were subjected to the thermal desorption spectroscopic analyses to examine an applicability of hydrogen as a tracer for evaluating the microstructure. The variation in hydrogen desorption characteristics with aging was discussed from the view points of microstructural changes. Experimental results revealed that the amount of hydrogen desorbed, CH, decreased monotonously as the aging proceeded and there was a relatively good correlation between the CH and Vickers hardness. The CH was expected to be a useful indicator for the material degradation. Additionally, the decomposition of the profile was attempted to understand the metallurgical meaning of hydrogen profile and apply the present method to the microstructural evaluation. As the result, it was suggested that the changes in two decomposed profiles with aging might reflect the variation of dislocation density and the precipitation process of M23C6 carbide and/or Laves phase, respectively.