Bioassay-guided fractionation of the EtOAc extracts of the epiphytic fungus Emericella nidulans resulted in the isolation of a mixture of two fatty acids. This mixture showed 98% binding affinity to human δ opioid receptor. These two fatty acids were identified as palmitic (PAM), 1, and linoleic acids (LNA), 2, by 1D NMR as well as by GC/MS analysis, after their methylation. We found that different ratio mixtures of 1 and 2 showed variations in selective binding activities to human δ opioid receptors. Five more fatty acids, arachidonic acid (ARA), 3, cis-4,7,10,13,16,19-docosahexanoic acid (DHA), 4, cis-5,8,11,14,17-eicosapentaenoic acid (EPA), 5, linolenic acid (ALA), 6, and γ-linolenic acid (GLA), 7, were evaluated for their binding affinity for opioid receptors. ARA, 3, displayed affinity to δ and μ human opioid receptors with 68% and 80%, respectively. GLA, 7, showed selective binding affinity to μ receptor with a value of 55%. These findings provide fascinating insight into the use of foods with high concentrations of fatty acids.