Abstract: Based on the mechanism of superoxide anion can be produced from the photosensitised riboflavin，three different concentrations（0.1，0.5，1.0 mmol ? L-1）of riboflavin were set to study the effect of exogenous reactive oxygen species（ROS）on‘Kyoho’grape berry development. The results showed that：the riboflavin could promote the development process of grape berry as the exogenous ROS，and the effect of 0.5 mmol ? L-1 treatment was the best，which resulted in sixteen days earlier of the grape berry ripening than the control. Content of soluble sugar and anthocyanin were increased after the treatment of 0.5 mmol ? L-1 riboflavin. At the same time，the hydrogen peroxide（H2O2）content，the pectinase（PG）activity，cellulase activity and lipoxygenase（LOX）activity were all increased at the early development stages of the berry，though the NADPH oxidase（NOX）activity was increased，considering the decreased superoxide dismutase（SOD）activity and production rate of superoxide ion，the increased H2O2 content might generate from other pathway such as LOX. However，the increase H2O2 content did not cause a cell damage（no significant differences of the MDA content）. All in all，the appropriate concentration of riboflavin could promote the grape berry ripening by activating the ROS production pathway.

Key words: grape, riboflavin, vitamin B2, reactive oxygen species, berry development, early ripening