Monkey head mushroom, Hericium erinaceum enriched diet fed to olive flounder Paralichthys olivaceus infected with Philasterides dicentrarchi afforded protection by enhancing the innate immune response. In the infected fish the scuticocidal activity, respiratory burst activity, and phagocytic activity did not significantly change at any time when fed with 0.01% H. erinaceum. However, on being fed with 0.1% and 1.0% enriched diets the chosen immune parameters significantly increased from week 1 to 4 when fish and challenged with parasites. The lysozyme activity significantly increased more from weeks 1 to 4 in the infected group than in the control. The cumulative mortality was 90% in control group whereas it was 45% and 30% when fed with 0.1% and 1.0% enriched diets respectively. The present study suggests that feeding with 0.1% and 1.0% enriched diets enhanced the immune parameters and affords protection from P. dicentrarchi infection in olive flounder.