To observe the changes of species and contents of free radicals generated by burning moxa with different storage time， and discuss the security of moxa from free radicals perspective. Methods: Detected and analysed free radicals in burning Qichun moxa sticks with 1 year， 3 years， 5 years storage time respectively using electron spin resonance (ESR) technique. Results:1) Free radicals were detected in both tar and gas phase of burning moxa， mainly quinone/semiquinone radicals in tar and alkyl， alkoxy， NO radicals in gas; 2) the signal intensity of all detected free radicals in burning moxa with 3 years and 5 years storage time was inferior to it in 1 year moxa(P<0.05， P<0.01)， quinone/semiquinone radicals， alkyl and alkoxy radicals had no difference between burning 3 years moxa sticks and 5 years moxa sticks (P>0.05)， while the signal intensity of NO radicals in 5 years moxa was under that in 3 years moxa(P<0.01). Conclusion: The free radicals generated from burning moxa mainly were quinone/semiquinone radicals， alkyl and alkoxy radicals， and NO radicals， free radicals mentioned above were less in burning moxa with 3 years and 5 years storage time than that in 1 year storage time moxa. The detection of free radicals might become an important evaluation basis for identification of moxa with different storage time and moxibustion security authentication.