||Interleukin-12 (IL-l2), a disulfide-linked heterodimeric cytokine, was purified from the supernatant fluid of Epstein-Barr virus (EBV)-transformed human B lymphoblastoid cell line. Shortly after IL-12 was identified, it was demonstrated that IL-12 possessed the ability to induce production of lymphokines, enhance cytotoxic activity and increase proliferation of T and NK cell in cooperation with other stimuli. All these property indicated that IL- 12 might exert anti-tumor effects against a variety of malignancies through immune mechanisms. Normally, IL-12 was expressed in mammalian cells. Using the capacity of Baculovirus expression system to perform many post-translational modification which are necessary for the expression of functional protein, we cloned IL-12 by inserting the two DNA fragment encoding IL-12 two subunits into a dual promoter vector pPLSP respectively. The Sf21 cells were transfected with yielded plasmids containing p35 and p40 subunits. The expression product was confirmed to be heterodimeric IL-12 and its strong effect on activated T and NK cell proliferation was assayed. Generally, co-transfection was carried out when expressing IL-12, we tried to clone p35 and p40 into pPLSP downstream from each promoter. It was demonstrated that this method is an efficient way to yield IL-12 not only for its high product amount also for the decreased time needed.