Effect of some radical scavengers on the breakage of DNA by ascorbic acid of ascorbic acid and Cu2+ was examined with sucrose density gradient centrifugation or viscometry. The degradation of DNA by ascorbic acid was distinctly inhibited by 2-aminoethylisothiouronium bromide. Even in the presence of Cu2+, the breakage of DNA by ascorbic acid was impreded to some extent by ethyl alcohol, sodium formate or nitrous oxide of relatively higher concentration. However, effect was seldom observed with potassium thiocyanate. Thus, it was suggested that certain free radical might be concerned in the breakage of DNA by ascorbic acid.