Abstract: The nutritive value of sainfoin (Onobrychis viciaefolia) hay harvested at vegetative, flowering, late maturity stages was evaluated by chemical composition and in vitro gas production techniques. In vitro gas production was determined at 0, 3, 6, 12, 24, 48, 72 and 96 h incubation times and their kinetics were described using the equation p = a+b(1-e-ct). Maturity had a significant effect on the chemical composition. Neutral Detergent Fibre (NDF), Acid Detergent Fibre (ADF) and Acid Detergent Lignin (ADL) contents increased with increasing maturity whereas Crude Protein (CP), ash and Condensed Tannin (CT) contents decreased. Maturity stage had also a significant effect on in vitro gas production and estimated parameters except for gas production rate (c).