The energy values of commercial laboratory animal diets have been customarily calculated by applying physiological fuel values (PFV) in this country. In order to ascertain accuracy of this application, apparent digestibility of crude protein, crude fat, nitrogen-free extracts (NFE), carbohydrate (NFE+crude fiber) and nitrogen-corrected metabolizable energy (MEn) of 10 commercial diets were determined using rats, dogs, rabbits and guinea pigs, respectively, and true digestibility of crude protein and crude fat of 12 feed ingredients was determined using rats. Apparent digestibility of the nutrients in the diets decreased with an increase in the crude fiber content of the diets. MEn values of the diets ranged between 2.18 and 3.75 kcal per g dry matter depending upon the crude fiber content of the diets. The energy values of the 10 diets calculated using PFV values of 4 kcal/g for protein and carbohydrate and 9 kcal/g for fat were compared with each MEn. The calculated values were 1.04 to 1.39 times higher than those of the respective MEn. All of the diets and most feed ingredients did not show high digestibility of nutrients assumed for the application of PFV. Therefore, it is concluded that application of PFV to the diets results in over-estimation of energy values and use of PFV for commercial laboratory diets in our country is not warranted. It is advisable to use MEn to evaluate energy value of commercial laboratory animal diets.