Calcitriol has important immunomodulation action and can prolong recipient survival after organ transplantation. The data in this study demonstrated that treatment of liver allograft recipient with calcitriol can protect allograft from acute rejection and prolong recipient's survival. Calcitriol inhibited expression of proinflammatory cytokine such as Interleukin-2 and Interferon-gamma intragraft. It also inhibited expression of nuclear factor kappaB (NF-kappaB) significantly as a result of enhancing its inhibitory protein I kappa B (IkappaB). As well, expression of zinc-finger protein A20 (A20) was enhanced significantly. The results suggest that calcitriol exerts its immunosuppression action in part through inducement of the A20, IkB, inhibition of NF-kB, and resultant proinflammatory expression pathway.