Objectives: The present study was aimed to find the effect of growth age period of Plantago major leaves on the biochemical composition of the plant. Methods: Leaves of P. major have been assessed for it is total phenolic, total flavonoid and total tannin contents at different growth age period (vegetative and generative). Results: revealed significant differences in biochemical compositions between two growth age periods of the plant, generative leaves exhibited significant amount of flavonoid (0.12__ampersandsignplusmn;0.002 mg QE\g DW) and tannin contents (0.12__ampersandsignplusmn;0.002 mg GAE\g DW) while a significant total phenolic contents were expressed by vegetative leaves (0.015__ampersandsignplusmn;0.001 mg GAE\ g DW). Conclusions: The research findings emphasized great effect of growth age period on biochemical composition of the P. major leaves.