A growing number of researchers have recognized the importance of using lipopolysaccharide (LPS) as target for the prevention and treatment of sepsis. However, no drugs targeting LPS have been applied clinically. In this study, LPS-inhibiting aptamers were screened by Systematic Evolution of Ligands by Exponential Enrichment (SELEX), and their therapeutic effects for experimental sepsis were observed. After 12 rounds of screening, 46 sequences were obtained. Primary structure analysis indicated that they had identical sequences, partly conserved sequences, or non-conserved sequences. Secondary Structure analysis showed these sequences usually contained hairpin or stem-loop structures. Aptamer 19 significantly decreased NF-kappa B activation of monocytes challenged by LPS and reduced the IL-1 and TNF-alpha concentration in the media of LPS-challenged monocytes. Furthermore, aptamer 19 significantly increased the Survival rate of mice with endotoxemia. The results suggest that a novel LPS antagonizing aptamer was obtained by SELEX, which successfully treated experimental sepsis. (C) 2009 Elsevier Inc. All rights reserved.