Condensed tannins (CT) from grape seeds (Vitis vinifera L.) were added to complex the protein fraction of Lupinus angustifolius seeds. Three CT/protein ratios were used: 96 mg/g (T1), 180 mg/g (T2) and 0 mg/g (T0). The CP losses in the rumen were assessed by the nylon-bag technique and CP intestinal digestibility (CPID) was estimated using an in vitro assay applying a three-step procedure: samples were subject to rumen degradation (in situ, 16 h) and the remaining residues were subject to the digestive enzymes of the abomasum and pancreas in vitro. A positive effect (p < 0.05) of the level of CT on the immediately soluble faction a and the insoluble degradable fraction b was observed between T0 and T2. In the presence of CT the rumen degradation rate was reduced (p < 0.05) from 0.0763/h (T0) to 0.0443 /h (T2). The application of CT showed a reduction (around 10 % for T1) of effective rumen CP degradability. The CPID did not seem to be affected (p > 0.05) by the presence of CT. These findings suggest that the use of grape seed CT might have the potential to improve the efficiency of utilisation of the protein fraction from lupin seeds.