Eating a diet high in fat can lead to negative health consequences, including obesity and insulin resistance. Omega-3 polyunsaturated fatty acids (such as those found in fish oil) prevent high fat diet-induced obesity and insulin resistance in rats. Eating a high fat diet also enhances sensitivity of rats to the behavioral effects of drugs that act on dopamine systems (e.g. quinpirole, a dopamine D2/D3 receptor agonist). To test the hypothesis that dietary supplementation with fish oil prevents high fat diet-induced enhanced sensitivity to the behavioral effects of quinpirole (0.0032–0.32 mg/kg), male rats ate standard laboratory chow, high fat chow, standard chow with fish oil, or high fat chow with fish oil (20% w/w). After 5 weeks, rats eating high fat chow were more sensitive (e.g. leftward shift of the quinpirole dose–response curve) than rats eating standard chow to yawning induced by quinpirole. Dietary supplementation with fish oil prevented this effect. That is, quinpirole dose–response curves were not different between rats eating high fat chow supplemented with fish oil and standard chow fed controls. These data add to a growing literature showing the complex relationship between diet and dopamine systems, and the health benefits of fish oil.