Sainfoin (Onobrychis viciifolia) is a temperate legume which contains condensed tannins (CT), i.e. polyphenols that are able to bind proteins and thus reduce protein degradation in the rumen. Few studies exist that investigated the relation between plant phenology, CT characteristics and nutritive value of sainfoin. Plants were harvested on 9 dates in the first and 4 dates in the second growth cycle. Phenological stages were analysed for leaf-to-whole-plant ratio, nitrogen (N), organic matter digestibility (OMd) by the pepsin-cellulase method, cell-wall concentration, N solubility (solN) plus CT concentration, biological activity and structures. Three sainfoin varieties (Esparcette, Ambra, Villahoz) were compared with a tannin-free legume, lucerne (Aubigny). Leaf-to-whole-plant, cell-wall concentration, N of sainfoin and lucerne were closely related with the phenological stage. Although sainfoin developed earlier than lucerne, its pepsin-cellulase digestibility was higher or close to lucerne. Esparcette had the lowest OMd, N and solN and the highest CT concentration. CT concentration, proportion of prodelphinidins (PD) and mean degree of polymerisation (mDP) increased with the phenological stage (or plant maturity) and these parameters were associated with lower biological activity of CT. Sainfoin varieties differed in their relationships between phenological stages, nutritional parameters and CT characteristics. The results demonstrated that sainfoin can be a valuable alternative forage legume to lucerne