Abstract: Hydroxyl radical (•OH) can cause severe damage to cells and tissues. However, its analysis is very difficult for its high reactivity and very short life. This paper present a HPLC-MS/MS method for indirectly detecting •OH by determining DMPO-OH, its addut with spin trap DMPO ( 5,5-dimethyl-1-pyrroline N-oxide ), with the N-Methyl-2-Pyrrolidone (NMP) used as internal standard. The ratio of the peak area of the DMPO-OH and NMP negatively correlate with the concentration of •OH. The results show that the method is simple, rapid, precise in both the determination of •OH and evaluation of •OH scavenging activities of antioxidants.