Morin is a flavonoid present in fruits and Chinese herbs. Based on in vitro studies, morin has been reported to show various beneficial biological activities. However, there is growing evidence that conjugative metabolism is central to the biological fate of flavonoids. Therefore, the biological effects of morin could be primarily determined by its conjugated metabolites. In this study, the effects of morin and its sulfates/glucuronides on the production of nitric oxide (NO) and cytokines from lipopolysaccharide (LPS)-activated macrophages were individually investigated and compared. The results indicated that the 50% NO production was inhibited from LPS-activated RAW 264.7 cells by 1.25 mM morin and 1.25 μM morin sulfates/glucuronides. Meanwhile, the 50% inhibition concentration (IC₅₀) values of morin and morin sulfates/glucuronides in activated peritoneal macrophages were 1.5 mM morin and 1.5 μM morin sulfates/glucuronides, respectively. In addition, 30% of the tumor necrosis factor-α (TNF-α) and 35% of the interleukin (IL)-12 productions from activated macrophages were inhibited by 2 ∼ 2.5 mM morin and 2 ∼ 2.5 μM morin sulfates/glucuronides, respectively. Furthermore, phagocyte activities in the peripheral blood of those for mice dosed with morin for two months were about 65 ∼ 70% of controls. Lower NO production and reduced macrophage phagocytic activities corresponded to LPS-resistant state. These findings indicated that morin may exhibit anti-inflammatory activity and reduced the incidence of experimental septic shock through decreasing the functions of macrophages and may regulate immune response through modulating the cytokine profiles. Therefore, morin could be a promising therapeutic candidate for inflammatory disease due to the strong activity of its metabolites.