Objective To provide experimental evidence for the exploitation of cinnamaldehyde as a kind of root canal disinfectant through studying the effect of cinnamaldehyde on endotoxin in root canals. Methods This experimental model of periapical periodontitis was established with Wistar rats. The 75 rats were divided randomly into 3 groups: Group of cinnamaldehyde, group of formaldehyde cresol formocresol, group of physiological saline. The level of endotoxin was measured by quantitative chromogenic tachypleus amebocyte lysate method before and after sealing the drugs in the root canal. Results The level of endotoxin in the group of cinnamaldehyde and formaldehyde cresol formocresol decreased obviously（P0.05）, the group of physiological saline was of no significant difference（P>0.05）. Conclusion Cinnamaldehyde can decrease the level of endotoxin obviously.
