Nowadays, one of the limiting factors in aquaculture is infectious diseases which cause substantial economic losses worldwide. Antibiotics are mainly used to control these diseases even though they have several adverse effects on the environment and human life. In this context, researchers are trying to find an alternative to antibiotics, which should be eco-friendly and economically feasible for fish farmers. Medicinal plants can be used as an alternative to antibiotics, which have been showing promising possibilities in numerous fish health benefits including modulation of the fish immune system (one of the most commonly purported benefits). This review describes the immunomodulatory role of different medicinal plants to boost the immune system of fish, which might be effective to fight against infectious diseases.