The aim of this study was to determine the potential nutritive value of a wild narrow-leaved clover (Trifolium angustifolium) hay harvested at 3 maturity stages (pre-flowering, flowering and seeding) in terms of chemical composition and in vitro gas production. In vitro gas production of Trifolium angustifolium hay was determined at incubation times of 0, 3, 6, 12, 24, 48, 72 and 96 h and the gas production kinetics were described using the equation y = a + b (1-e(-ct)). Maturity had a significant effect on both chemical composition and in vitro gas production kinetics. Neutral detergent fibre (NDF), acid detergent fibre and condensed tannin (CT) concentrations increased with maturity, while crude protein (CP) concentration decreased from 16.9% pre-flowering to 13.2% at seeding. The condensed tannin concentration of Trifolium angustifolium hay ranged from 2.16 to 3.71%.