For the first time the identification and quantification of phenolic compounds of the Olea europaea L. cv. Chemlali olive were carried out to examine their profile during maturation. The phenolic composition was studied by using reverse-phase high-performance liquid chromatography during all steps of fruit development. Oleuropein is the abundant phenolic compound in Chemlali olive, and its concentration increases during maturation. An indirect relationship between oleuropein content in olive fruit and hydroxytyrosol was observed. Weak changes in the amounts of the other phenolic monomers and flavonoids were also observed. The total phenolic content varied from 6 to 16 g/kg expressed as pyrogallol equivalents. Its highest level was found at the last maturation period. The antioxidant capacity of olive extracts was evaluated by measuring the radical scavenging effect on 1,1-diphenyl-2-picrylhydrazyl. The IC(50) values of the olive extract ranged from 3.2 to 1.5 microg/mL. There was a correlation between antioxidant activity and total phenolic content of samples. The antioxidant activity increased with maturation. This could be attributed to the increase of the tolal phenol level with fruit development.