The production of.OH in the mixture of BLMA(5), Fe(2+) and O(2) has been detected by ESR spectroscopy and the degradation of DNA induced by BLMA(5), in the presence of Fe(2+) and O(2), has been detected by TBA reaction. When Fe(2+) was replaced by Cu(+), Cu(2+) or Fe(3+),.OH was not producted and DNA not degraded.OH scavenger could scavenge.OH effectly but had little effect on the DNA degradation. Reducing agents could scavenge.OH but enhanced the DNA degradation. SOD could scavenge.OH but inactivated SOD showed no effect on.OH. Both SOD and inactivated SOD could inhibit the degradation of DNA.OH reacted more readily with bases than with deoxyribose, while the main injury of DNA induced by BLMA(5) was the destruction of deoxyribose. The results suggest that.OH was generated in the mixture of BLMA(5), Fe(2+) and O(2) but not the key factor which initiated the degradation of DNA. It could be the activated BLMA(5).Fe(2+).O(2) complex that induced the degradation of DNA.