This study examined the effectiveness of 2 different dosage levels of a fish hydrolysate, a natural supplement derived from fish protein, in reducing fear and anxiety in beagle dogs. A thunderstorm model was used, which entailed playing a recorded track of a thunderstorm to elicit measures in an open field test. Fear and anxiety were assessed with behavioral measures, which included noise induced activity and inactivity and an observational behavioral assessment, and blood cortisol levels. The test compound showed some effectiveness in reducing a hyperactivity response to thunder and in reducing the cortisol response. The results of this study provide initial support for considering the use of fish hydrolysate as a dietary supplement to reduce fear and anxiety.