Three rumen and proximal duodenum cannulated Jersey heifers were used in a 2×3×3 Latin square design experiment to determine the effect of rapeseed oil supplementation on ruminal and intestinal protein digestibility of rapeseed meal, soyabean meal and lupin seed. Rapeseed oil at 0, 100, 200, 300, 400, 500 g/day was infused into the rumen cannula. The ruminal degradation of protein was estimated by using rumen nylon bags (in sacco method), the intestinal digestibility of rumen undegraded protein, by the mobile nylon bag method. A high level of rapeseed oil (400 and 500 g) significantly decreased effective degradability and increased intestinal digestibility of rapeseed meal and lupin seeds. Lower levels of oil (100, 200, 300 g) did not significantly affect protein degradation in the rumen or intestinal digestibility.