Tannins level as total phenols (TP), condensed tannins CT), hydrolysable tannins (HT), phytic acid (PA), cell-wall constituents [neutral-detergent fiber (NDF), acid-detergent fiber (ADF)], total nitrogen and nitrogen forms [buffer soluble nitrogen (BS-N) and non-protein nitrogen (BS-NPN)] were determined in leaves and stalks of Sesbania aculeata and Kochia indica harvested 60, 90, 120 and 150 days after planting. The NDF, ADF, TP and HT concentrations significantly increased and BS-N, BS-NPN and total nitrogen concentrations significantly decreased at the late harvest stage of both S. aculeata and K. indica. Phytic acid and CT concentrations significantly increased with age of S. aculeata. The CT concentrations in K. indica were notably low (0.05 g/kg DM) during the maturity stages. In both plant species, NDF and ADF concentrations were positively correlated with TP and HT but negatively correlated with BS-N, BS-NPN and total nitrogen. NDF and ADF concentrations were positively correlated with CT and PA for S. aculeata but negatively correlated with PA for K. indica. Harvested plants at early maturity stage after 90 days of planting were judged to be nutritionally better for ruminants.