The in vitro effect of Astragalus radix water extract on the non2specific immune responses of macrophages isolated from the head kidney of Cyprinus carpio was evaluated. Astragalus radix extract stimulated the proliferation of the head kidney macrophages , and it alone had no effect on nitrogen burst activity of macrophages. But it enhanced the nitric oxide production of the mixture of macrophages and granulocytes induced by LPS. It is suggested that Astragalus radix could modulate the non2specific immune response of Cyprinus carpio.