A Tenebrio molitor larva that is called mealworm is widely used as feed for raising a pet. Also, it is the insect that would be produced as the edible food for human. For these reasons, many researchers are revealing about physiologic characteristic of Tenebrio molitor to make good use of it. However, morphological characteristic of different larval stage is not specifically indicated and researchers have different opinions about the average number of Tenebrio molitor’s instar until now. This study, therefore, was carried out to examine the physiological and morphological characteristics of Tenebrio molitor larva in different larval stages, and the average number of Tenebrio molitor’s instar. As a result, all of the Tenebrio molitor larvae had 7~8 days during their incubation period and 3~4 days during the 1st instar period. After the 1st instar, there were comparatively large differences in the number of days in each instar. Before emergence, most of the larvae comparatively showed 15th~17th instars, particularly, the largest rate of pupae (28.83%) was observed in the 17th instar. In terms of the body length of each Tenebrio molitor larval stage, the body length was gradually increased by the 17th instar. Beyond the 17th instar, however, the body length was smaller than 17th instar. In the 1st instar, the larva had white color, and the color gradually changed into brown from the 2nd instar. Through this study, we could identify the accurate incubation period, 1st instar period, the average number of instar, body length and the color change in different larval stages. These results would be used as a fundamental data for further study about the physiological and morphological characteristic of each instar period.