Samples of leaves, stems and whole plant of tetraploid Robinia pseudoacacia harvested at four different growth stages (first rapid growth, slow growth, second rapid growth, and leaf-colour changing) were analysed for chemical composition and in situ disappearance of protein and fibre using the nylon bag technique. The crude protein content was the highest in leaves, followed by whole plant, and the lowest in stems, while the opposite trend was found for dry matter, NDF, and ADF. Moreover, the crude protein content of the three plant parts decreased during maturation. Effective degradability of crude protein was higher for stems (519.0 g kg^-1) than for whole plant (353.6 g kg^-1) and leaves (270.4 g kg^-1). Effective degradability of ADF was significantly higher in leaves than in the whole plant and stems. Ruminal disappearance of nutrients in the three plant parts was higher during the first rapid growth stage than at later stages.