The sustainable animal production systems, based on pastures require the knowledge of animal and vegetation responses to different management strategies (Oliván and Osoro, 1997). The lack of knowledge about the grazing behaviour, intake and diet digestibility of “Alentejano pigs” explored under “Montanheira”, leads to many doubts about the most adequate production strategies. N-alkanes are components of plant cuticular wax and have been successfully used as markers for estimation of intake in ruminants (Dove and Mayes, 1991), however few studies with pigs have been published, particularly “alentejano pigs”. In the “Montanheira” system, the main components of the diet are acorns and pasture. Therefore this trial was conducted to validate the use of the n-alkane technique to estimate intake and digestibility of the particular diet composition of “Montanheira” (acorns and pasture) by “Alentejano pigs”.