This work evaluates the phase transformations during aging of an UNS S31803 DSS at 650ºC and its influence on the DOS. The material was solution treated at 1175ºC and then aged at 650ºC for times up to 360 h. SEM-BSC images indicate the formation of Cr2N, σ and χ phases in the samples aged at 650ºC. The analysis of DL-EPR curves, obtained in a 1 M H2SO4 + 0.25 M NaCl + 0.01 M KSCN solution, shows an increase in DOS values for samples aged at 650ºC. Probably, this increase observed in DOS values is mainly related to the presence of Cr- and/or Mo-depleted α, as a result of σ phase, χ phase and/or Cr2N formation at 650ºC. Moreover, a possible healing up of Cr- and/ or Mo-depleted areas is observed between 1 h and 4 h of aging at 650ºC.