From the concept of sustainability and the multifunctionality role attributed to the European farming systems, a first approach to the analysis and discussion of the relationship between the labour productivity, as partial indicator of the economic sustainability of the livestock farms and its environmental function was made. A sample of 11 sheep farms that use a Natural Park, representative of four farm groups established in a previous study by means of multivariate statistical analysis, was studied. For each farm, economic results and an indicator of family labour productivity, the relative levels of grazing and the relations between the farms and the market and the agro-sylvopastoral systems were calculated . These results show that there is not a clear relationship between the levels of the indicator of economic sustainability of farms and their environmental function.