The protecting effect of (−)-epicatechin (EC), (−)-epicatechin gallate (ECg), (−)-epigallocatechin (EGC), (−)-epigallocatechin gallate (EGCg) and 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) on the DNA strand scission induced in tritiated water was analyzed. The scission with the hydroxyl radical produced by the decomposition of water molecules was decreased by the addition of above reagents. Protective effect of EGCg, EC and DMPO was dependent on their concentrations, but that of ECg and EGC was independent. Therefore, it was considered that certain amounts of ECg, EGC molecules might locate around DNA molecules, interacting with DNA.