The aim of this study was to quantify antioxidant substances and chlorophyll content, as well as to measure the antioxidant activity in cassava leaf flour (CLF) of different cultivars at several plant ages, in order to lead to a higher utilization of these leaves, and consequently to an enhancement of this agricultural by-product. The contents of antioxidant substances (vitamin C, polyphenols and β-carotene) were regarded as high and increased as the plants matured. The chlorophyll content decreased with plant maturity and presented a negative correlation with antioxidant substances, which indicates that the highest antioxidant levels are found when the plant presents low chlorophyll levels. CLF showed a high antioxidant activity when the lipid oxidation inhibition method (β-carotene/linoleic acid) was used, and moderate when the free radical capture method (ABTS) was used. The main contribution to the CLF antioxidant activity seems to be provided by vitamin C, which presented the best correlation with the ABTS test. Out of the ages studied, that of 14 months presented the highest antioxidant levels; Mocoto and Pao da China cultivars stood out the most. Key words: Cassava leaf flour, antioxidant activity, antioxidant substances.