Objective To illuminate energy demands of Mongolian gerbil by analyze the diversity in intestinal morphology and the energy metabolism of different species. Methods 10 SD rats, 10 ICR mice and 10 mongolian gerbils were feed individually in metabolic cages. Gather and measure the energy of their feces and urine in 24 h for 5days. Then, all the animals were weighed and anaesthetized, collect and measure the length of the intestine. Results Rats digestive energy and metabolic energy respectively are 314.56 kJ/d and 314.55 kJ/d, mice are 10.608 kJ/d and 9.799 kJ/d, gerbils are 99.828 kJ/d and 99.927 kJ/d. Rats digestive energy and metabolic energy used to increase body weight respectively are 19.273 kJ/g and 18.831 kJ/g, mice are 71.842 kJ/g and 72.390 kJ/g, gerbils are 56.142 kJ/g and 55.965 kJ/g. In these animals, the length of gerbils' digestive tract is the shortest, the length of rats' small intestine is the longest, and the percentage of gerbils' appendix is the largest. Conclusions There are significant differences in the length of the gut and energy needs.