We examined the effects of Prunella vulgaris Labiatae (P. vulgaris L.) on specific and non-specific immune responses of Nile tilapia, Oreochromis niloticus. The optimal concentration without toxicity of P. vulgaris was determined to $30-40{mu}g/ml$ in vitro and $120{mu}g$/100 g of fish in vivo. P. vulgaris significantly elicited an antibody titer compared to FCA or ${eta}$-glucan. ${eta}$-glucan plus P. vulgaris group synergistically enhanced antibody production. No significant difference in antibody production was observed between P. vulgaris and P. vulgaris plus ${eta}$-glucan group. A respiratory burst activity of head kidney (HK) leucocytes of tilapia administered with 300 or $500{mu}g$ P. vulgaris was significantly (p < 0.05) enhanced compared with the PBS-injected control group and FCA-treated group. Maximum increase in the NBT reduction value was observed in $500{mu}g$ P. vulgaris group but no significant difference was found between 300 and $500{mu}g$ P. vulgaris group. The level of serum lysozyme activity was significantly (p < 0.05) higher in the 300 and $500{mu}g$ P. vulgaris than $100{mu}g$ P. vulgaris and FCA group. The phagocytic activities of HK leucocytes from tilapia administered with 300 and $500{mu}g$ P. vulgaris were significantly (p < 0.05) higher than $100{mu}g$ P. vulgaris and the control group. P. vulgaris was revealed with a good immunoadjuvant evoking the specific and non-specific immune responses of tilapia.