Mixing rates of powdered raw materials of welding electrodes were measured using technetium-99m adsorbed raw material components as tracer. (1) Adsorbed technetium-99m was not detached during studies. (2) Taking more than 10 samples of the smallest possible but equal size at definite mixing stages were important in assuring reliability. (3) Mixing rates were independent on mixing ratio of the two components insofar as the specific gravity and grain size are same. (4) Mixing rates were inversely proportional to the specific gravity and grain size but proportional to mixing ratios in case of the specific gravity difference was more than 1.5. (Author).