Free radicals exist both in human body and cigarette smoke, in the forms of many species, i.e. superoxide radical (O-·2), hydroxyl radical (HO·), alkyl radical (R·), alkoxyl radical (RO·) or alkyl peroxyl radical (ROO·), there is no doubt of their pathophysioligical reaction and oxidative damage. Electron paramagnetic resonance (EPR) in conjunction with spin trapping technique is a selected method for free radical detection and quantification. Ginkgo biloba leaves extract (EGB), a phytomedicine mainly composed of flavonoids, terpenoids and proanthocyanidins, is potential in free radical scavenging and antioxidant. In current paper, the scavenging effect against chemical/biological system radical (DPPH, HO·, O-·2) and cigarette smoke radical (gas-phase and particulate-phase radical) for EGB and EGB cigarette have been studied using EPR method, respectively. Several selected flavonoids (Quercetin, Rutin) and Proanthocyanidin also have been assayed and compared. The results show that EGB is managed to scavenging free radical originated by chemical/biological system and cigarette smoke. Although inhibitory capacity is weaker than flavonoids and proanthocyanidin, EGB is obtained easily through extraction and can be developed to natural antioxidant and free radical scavenger in food and tobacco. EPR is a reliable tool in free radical scavenging duing to its good sensitivity and high stability. The spin trap DEPMPO exhibits superiority in trapping superoxide radical and PBN is more efficient in trapping smoke gas-phase radical than DMPO. The mechanism of EGB scavenging free radical has been discussed, multiple phenolic hydroxyl groups are the main reason.