Objective: To express recombinant human IL-12 which has the activity of stimulating the proliferation of T cells in vitro by baculovirus/insect cell system. Methods: Insert p35 and p40 cDNA into baculovirus transfer vector pAcUW42, then co-transfect insect Sf9 cells with AcUW1.lacZ baculobvirus DNA for constructing IL-12 expression recombinant baculovirus by homologous recombination. Results: Culture supernatant of Sf9 cells infected by IL-12 recombinant baculovirus which selected by a series of assay of baculovirus plaques, ELISA and Western Blotting, could stimulate the proliferation of T cells from normal human peripheral blood as standard IL-12 did. Conclusion: We have established the IL-12 baculovirus/insect cell expression system whose product has the activity of stimulating the proliferation of T cells in vitro