Background: Clindamycin phosphate (CLDMP) is effective against Gram-positive and anaerobic bacteria, and is known to have anti-inflammatory properties. Methods: To further study the anti-inflammatory properties of CLDMP, we examined the scavenging effects on superoxide anion and hydroxyl radical using an electron spin resonance (ESR) spin trapping method. Results: In a hypoxanthine-xanthine oxidase reaction system, CLDMP did not scavenge superoxide anion. In a Fenton reaction system, however, CLDMP reduced the level of hydroxyl radical, and the scavenging activity of CLDMP against hydroxyl radical was more potent than that of mannitol. As the concentration which inhibits the formation of hydroxyl radical by 50% (IC50) of CLDMP was changed by the addition of a 10-fold amount of a spin trapping agent, 5,5-dimethyl-1-pyrroline-N-oxide, it is strongly suggested that CLDMP scavenges hydroxyl radical directly. Conclusion: This is the first report of the direct scavenging effect of CLDMP on hydroxyl radical, and the effect may improve the inflammatory response caused by invading bacteria.