Endodontic infection in root canals is a major cause of chronic inflammation of periapical bone. Dynamic variations of extra-cellular matrix molecules in chronic inflammation indicate not only disease activity but also the prognosis of each condition. Recently, hyaluronan was utilized as a biomarker in osteoarthritis and periodontal disease cases. Objective: The purpose of this study was to determine the correlation between bacterial colonization and hyaluronan concentration in root canal exudate. Methods: Exudates of 10 single root canals with endodontic infection were collected twice (one week after biomechanical instrumentation and two weeks later). The experiment was divided in two parts. In the first part we determined hyaluronan concentration by the ELISA technique. In the second, we measured bacterial cultures on blood agar plates by counting the total number of bacterial colony-forming units per ml of transfer medium in both aerobic and anaerobic conditions. The correlation coefficient of hyaluronan concentration and bacterial colonization was analyzed by using Spearman's test. Results: Although three samples were lost, five out of the remaining seven samples had positive correlations. However, none were significant. The correlation coefficient and p value for hyaluronan and total bacterial colonization were 0.25 and 0.49 respectively; those for hyaluronan and anaerobes were 0.46 and 0.18; those for hyaluronan and aerobes were –0.11 and 0.75. Conclusion: We concluded that hyaluronan concentration could be measured in root canal exudate.A further study with a larger sample size may support hyaluronan as a useful biomarker of disease activity in endodontics. This study was supported by faculty of Dentistry, Chiang Mai University, Thailand.