Objective: To investigate the effect of activated protein C (APC) on inflammatory responses in human umbilical vein endothelial cells (HUVEC) stimulated with lipopolysaccharide (LPS). Methods: The second passage of collagenase digested HUVEC was divided into the following groups: serum free medium control group (SFM control), phosphate buffer solution control group (PBS control), LPS group with final concentration of 1 μg/ml (LPS group), APC group with final concentration of 7μg/ml, Pre-APC group (APC pretreatment for 30 min prior to LPS challenge), and Post-APC group (APC administration 30 min after LPS challenge). Supematant was harvested at 0, 4, 8, 12 and 24 h after LPS challenge. Interleukin-6 (IL-6) and Interleukin-8(IL-8) levels were analyzed with ELISA. Cells were harvested at 24 h after LPS challenge, and total RNA was extracted. Messenger RNA levels for IL-6 and IL-8 were semi-quantitatively determined by RT-PCR. Results: Compared with control group,IL-6 and IL-8 levels steadily increased 4 to 24 h after LPS stimulation. APC treatment could increase LPS-induced IL-6 and IL-8production. The mRNA levels of IL-6 and IL-8 exhibited a similar change. Conclusion: APC can further increase the level of IL-6and IL-8 induced by LPS. The effect of these elevated cytokines is still under investigation.