Herbal immunomodulator is a substance which stimulates the compounds of immune system.A number of Indian medicinal plants have been reported in Siddha medicine to possess immunostimulatory effects and thus can act as efficient and potential source of drug for treatment of various diseases. The use of plant product for treatment of various human diseases has been mentioned in Indian medicines like Siddha and Ayurveda. Some of these plant products are believed to enhance the natural resistance of body against infection.Among these Siddha formulated medicine is one of the oldest medical systems in India. Siddha medicine become popular nowadays, it is used to treat various outbreaks of communicable diseases. One of the well known poly herbal decoction of Siddha medicine is “Kapa sura kudineer”. This review describes role of plant derived immunostimulants in various medicine and also discusses about the biological screening methods for various plant based drugs that reveals the mechanism involved in immune response.