Arginine vasotocin (AVT) is known to play an important role in the regulation of social behavior in a number of vertebrate species. Nevertheless, the relationship between AVT and intraspecific interactions appears complex and in some cases contradictory. Moreover, AVT influences other behaviors, which are not primarily social including exploratory behavior, locomotion and thermoregulation. Some of these behavioral effects may be side-effects from a general influence of AVT on physiology. Indeed AVT can regulate metabolism and osmoregulation. Because most studies have been conducted using mammals and birds, its role in modulating behavior in other vertebrate groups is largely unknown. In this study we examined the effect of AVT on the social behavior of male common lizards, Zootoca vivipara. Moreover, considering the variety of pathways AVT could be involved in, we investigated its consequences on thermoregulatory behavior and physiological performance. In mid June 2010, 74 males were captured from field sites (Mont-Lozere, South-eastern France) and kept in the laboratory for three weeks to obtain behavioral (reaction to conspecific odors, thermoregulation) and physiological (endurance, testosterone level) measurements. We demonstrated that injection of AVT reduced testosterone level and affected social behavior in different ways depending on the size of an individual. Specifically, small males injected with AVT were less attracted by conspecific odors than small control males, and no effect was detected in large males. Moreover, AVT promoted thermoregulatory behavior and enhanced endurance. These results are concordant with previous results obtained in this species in studies on stress suggesting that AVT may act through its influence on corticosterone secretion.