PURPOSE: To regenerate the performance of an electrophotographic CdS powder to a state same as that immediately after the preparation by heat treating the CdS powder deteriorated during long period storage after precipitation, in the presence of activated carbon at a specified temp. or lower for a week or more.

CONSTITUTION: When an electrophotographic CdS powder prepared by burning the CdS powder stored for a long period after precipitation, it is deteriorated in sensitivity, photodecay speed characteristics, etc., as compared with the one obtained by burning fresh CdS immediately after precipitation. This deteriorated CdS powder can be regenerated to impart photosensitive performance same as the one obtained by burning fresh CdS immediately after precipitation, by heat treating this deteriorated CdS in the presence of ≥1wt% activated carbon, especially, for use in vapor phase adsorption or desulfurization, in a gas-tight vessel out of contact with the air at ≤100°C, preferably, 50W70°C, for ≥1 week, and burning this CdS powder at 450°C like the conventional method.