The aim of this study was to investigate the influence of harvest season and nitrogen (N) fertilisation on chemical composition and digestibility of the herbage harvested from a mountain meadow (of the vegetation type Arrhenatheretalia). Four rates of N fertiliser (0, 60, 120 and 180 kg N/ha per year in a single spring application of calcium ammonium nitrate) were compared in field-replicated plots. The experiment lasted 7 years. During the first 3 years each plot was harvested twice per year (June and September) according to a traditional harvest system, whereas in the last 3 years (after a transitional year) each plot was harvested three times per year (spring, summer and autumn) following a more intensive harvest system. In both harvest systems, herbage collected in the first cut (early or late June) had higher fibre contents and lower digestibility (P < 0.001) than herbage collected in the regrowth. N fertiliser increased significantly (P < 0.001) the annual yield of herbage in the 2-harvest system, but did not affect (P > 0.10) herbage yield in the 3-cuts system. N fertiliser changed the botanical composition of herbage and promoted grass growth, resulting in increased (P < 0.05) fibre content and decreased (P < 0.05) digestibility and rate of degradation of herbage, these effects being variable in the different harvest seasons. Our results suggest that the more intensive management system without N fertilisation could be considered a suitable practice for the management of these botanically complex mountain meadows. These results may contribute to design fertilisation and management practices of mountain hay meadows to optimise their productivity and sustainability.