Different protein sources, defatted soybean flour, casein or whey protein concentrate, were used for the preparation of three protein pollen supplement diets to feed colonies of Apis mellifera carnica, during the winter season. The effect of studied protein pollen supplement diets on food consumption (%), sealed brood area (In²), pollen stores (In²) and honeybee strength (in terms of mean number of combs covered with bees) of the colonies were recorded. The results indicated that, the defatted soybean flour or whey protein concentrate pollen supplement diet was more consumed by the honeybee colonies than casein pollen supplement diet. Also, the highest areas of worker sealed brood, stored pollen and colony population density were observed with defatted soybean flour or whey protein concentrate pollen supplement diet. Casein pollen supplement diet was found to be the lowest consumed and showed the lowest biological activities among three tested pollen supplement diets. There was a positive relationship between the amount of diet consumed and the changes in worker sealed brood, stored pollen and colony population density. Defatted soybean flour or whey protein concentrate in pollen supplement diets of honeybees during winter season proved to be very effective and could be valuable to improve colony parameters.