Recently, cortisol has been suggested to moderate the positive relationship between testosterone and antisocial behavior. More precisely, high testosterone levels have been found to be related to aggressive or dominant behavior especially when cortisol levels were low. In the present study, we aimed to extend these findings to pro-environmental behavior as an indicator of prosocial behavior. In a first step, 147 male participants provided information on their everyday pro-environmental behavior by completing an online questionnaire on various energy-saving behaviors. In a second step, subjects provided two saliva samples for the assessment of testosterone and cortisol on two subsequent mornings after awakening. We found that testosterone was negatively related to pro-environmental behavior, but only in men with low cortisol. In conclusion, our findings provide first evidence for the joint association of testosterone and cortisol with everyday pro-environmental behavior. These results further reinforce the importance of considering interdependent hormone systems simultaneously rather than focusing on a single hormone.