Abstract: Objective:For further research of the effect of photodegradation of riboflavin to cells.Methods:The mean telomere length and the activities of telomerase were studied.MTT assay was used to estimate the inhibition rate of riboflavin.Immnohistochemical studies by detecting 8-hydroxyguanine（8-oxodG） as the marker of DNA damage.The telomere length was measured by southern blot.The activities of telomerase was measured by TRAP.Results:The result showed that The inhibition rate of tumor cells is dose-dependent of riboflavin;guanine could be oxidized into 8-hydroxyguanine in both 32 and 3.2μmol/L riboflavin-given groups;the telomere length was measured by southern blot and the results indicated that there was a continuous telomere shortens with time;in the time of 0,0.5,1,2,4h dealt with photosensitiv riboflavin,ratio of telomere shorten was 5.5%,11.2%,14%,17.8%.The activities of telomerase was lower at first 1h but had a trend to rise after that.Conclusion:The photodegrada-tion of riboflavin caused oxidized damage of G-rich region on DNA,which may related with the telomere shortening and the activities of telomerase.