Objective To investigate the expressions and significance of interleukin 8 (IL 8) in patients with ankylosing spondylitis (AS). Methods Using microarray and RT PCR to detect the expressions of IL 8 in peripheral blood mononuclear cells (PBMC), synovial fluid mononuclear cells (SFMC) and synovial cells in patients with active AS. Comparing the results with those in PBMC of both healthy volunteers and patients with rheumatoid arthritis (RA), and also with those in synovial cells obtained from patients undergoing knee operations for trauma. Results The expressions of IL 8 in PBMC and SFMC of patients with active AS were significantly higher than those in PBMC of the healthy controls. The expression of IL 8 in PBMC of RA patients was also higher than that of healthy volunteers. Higher expression of IL 8 in the synovial cells were detected in AS than that of patients with knee joint trauma. Conclusions The expression of IL 8 is high in patients with AS. The result may indicate that IL 8 is possibly one of the important mediators of inflammation in AS, and it may mediate the induction and development of inflammation in synovium or other tissues involved in AS