This study interested in a medicinal plant, Psidiumguajava with immunomodulatory action in order to determine which active ingredients contained in this plant act on immunity agents. We first presented the principles of herbal medicine, then the immunosuppressive and immunostimulant actions of the plant by studying the inflammatory reaction. The studies have enabled us to understand that within this plant, certain molecules have beneficial actions for the animal organism. These actions aim at restoring balance in the system and avoiding side effects. Along with other plants we noticed that Psidiumguajava plays several more specific roles, such as anti-inflammatory, immunostimulant or anti-tumor. The active ingredients of these immunomodulatory plants with known sites of action are interesting tools thanks to their multiple effects on the immune response and associated pathologies and thanks to their synergy within the magistral preparation. Thus, it is important to have various therapeutic tools as not to be confronted with certain clinical cases refractory to existing treatments.