The effect of thermal treatment, in air and in vacuum, on51Cr(III)-doped potassium chromate and on post-irradiation-recrystallized potassium chromate has been studied. The51Cr(VI) yield was found to increase and the M yield to decrease in all samples, while the DP yield remained constant up to 180 °C and decreased at higher temperatures. The results were not affected by the presence of oxygen.