Within the EEC MEDALUS II project, aimed at the study of the climate-water-soil-sward-grazing interactions on the desertification process, a trial was conducted in North Sardinia (Italy) to compare the effects on a natural pasture sward of two different management types (overgrazing vs no-grazing). The results of the 1st year experiment carried out in two homogeneous basins (10 ha each one) are reported in this paper. Wide differences were recorded on the sward characteristics due to the animal grazing. Surface sward height, available and residual dry matter at the end of the spring were higher in the ungrazed pasture than in the grazed one. The grazing reduced the percentage of grasses and legumes on green available DM. On average the covering rate was lower in the grazed basin. The most important botanical families were Compositae, Graminaceae and Liliaceae. The pastoral value (Daget and Poissonet method) was very low because of the presence of many species with low specific index (unpalatable and thorny species). The results showed the characteristics of the natural pasture in quantitative terms. The high amount of residual dry matter recorded at the end of the spring in the ungrazed basin in an important factor of fire hazard. The effects of overgrazing on soil erosion and desertification processes need to be studied for several years.