This study measured the digestibility of crude protein, crude fat, and dry matter in three protein sources: poultry by-product meal (PBPM), poultry viscera, and crushed mealworms using diatomaceous earth as an indicator. A control diet was made, and test diets were mixed in a 70:30 control diet:test ingredient ratio. Forty-four female mink housed in individual cages were fed experimental diets for 5 days, and fecal samples were collected and analyzed for nutrient residues compared to the diet composition to determine digestible nutrient levels. Mealworms had a greater dry matter digestibility (P < 0.01; 96.26%) than poultry viscera (77.29%) and PBPM (86.76%). PBPM had a lower fat digestibility (P < 0.01; 84.64%) than mealworms (94.78%) and poultry viscera (98.15%). There was no significant difference among treatments for protein digestibility. Using a standard nitrogen-to-protein conversion factor of 6.25, the crude protein content of the mealworms was 51.74%, although with an apparent digestibility coefficient of 0.77, this ingredient had an available crude protein composition of 39.70 ± 2.95. A nitrogen-to-protein conversion factor of 4.80 would be more accurate than 6.25 when using mealworms as a feed ingredient for monogastric animals.