Among animals, conflicts are resolved through agonistic behavior, an expression of which embraces a range of fleeing behaviors, displays, up to the extreme of physical combat. This study aims to establish an observation protocol and to describe the aggressive acts of Aegla longirostri. Aeglids were collected in the field and kept for one week of acclimation in individual fishbowls with no contact with other animals. A total of ten pairs of males were paired, the members of each pair differing by no more than 1 mm in cephalothorax length. The behavioral acts were described from the combats videotaped for 20 minutes with each pair, of which 16 were considered aggressive acts. The animals took an average of 198 seconds to start combat. A table of aggression intensity was established, ranging from −2 (fleeing) to 5 (intense combat). There was a significant difference between winners and losers in the time spent in the different levels of intensity and in the duration of the acts performed. Aegla longirostri showed very intense aggression with defined aggressive acts and continued to engage in agonistic behavior for the entire duration that was recorded. This is the first report of aggressive behavior in aeglids, it will be possible to carry out more profound studies on the behavior of these animals.