The influence of benzyladenine (BA, a cytokinin) on peroxidase activity during the senescence of sunflower cotyledons was investigated. For this purpose, changes in the activity of peroxidase were determined during senescence of the cotyledons by spectrophotometric method and the effect of BA on peroxidase isoenzymes was determined by polyacrylamide gel electrophoresis. However, the level of total chlorophyll was measured as the sign of senescence. While the senescence stage of cotyledons progressed, peroxidase activity was found increasing, whereas there was a decline in the level of total chlorophyll. In the BA-treated cotyledons, the activity of peroxidase and the number of isoperoxidases decreased compared with the control whereas the level of total chlorophyll was higher than the control.