The mice used in animal facilities belong to the family Muridae, subfamily Murinae, order Rodentia, genus Mus and species Mus musculus. They are social and territorial animals. Several lineages developed in the laboratory show aggressive behavior similar to that of wild mice. The aim of this study was characterize the hierarchical structure, body characteristics and hormonal levels in dominant, subordinate and non-aggressive mice. The model established for spontaneous aggression (MSA) evaluates the pattern of aggressive behavior (PBA) and categorizes the animals as follows: LAg - individuals with low aggressive behavior, HAg – dominant (highly aggressive) and Sb - subordinate. The regrouping of adult male mice produces substantial stress and influences the formation of their hierarchical structure. Behavioral comparisons before regrouping (BfR) and after regrouping showed that the percentage of body weight lost in mice was dependent of the specific categories as follows: LAg - 68.1%, HAg - 86.9% and Sb - 90.5%; the average corticosterone levels by category were BfR: 43.5±17.5, LAg: 177.0±40.4, HAg: 72.8±23.8 and Sb: 136.4±51.2 ng/mL. Dominant mice showed differences in body characteristics (primarily the body/tail relationship) relative to subordinate mice. Two additional hierarchical positions were observed: “neutral individual” (without aggressive behavior) and “subordinate target” (an animal that receives approximately 30% of the total number of attacks made by dominant animals).