Abstract: Four male Thai Brahman cattle (261±3.2 kg; 24-36 months old) were fed rice straw as a basal diet and Leucaena treated in one of three methods: untreated (control), Leucaena treated with NaOH solution, Leucaena+PEG (Poly Ethylene Glycol). Using Leucaena treated with NaOH solution as a supplement improved (p<0.05) fibre digestion but N-balance reduced (p<0.05). Whilst N-balance, N-digestibility and fibre increased (p<0.05) but Dry Matter (DM) digestibility decreased (p<0.05) when animals supplemented with Leucaena+PEG. The effect of Condensed Tannins (CT) in Leucaena depends on the treatment of Leucaena, NaOH solution and PEG. Using NaOH solution treatment is potentially beneficial for improving fibre digestion but N-balance was reduced. However, adding PEG beneficial for improving fibre digestion, N-balance and N-digestion but DM digestion decreased.