Andean grasslands of the La Araucania Region are used every year by Pehuenches communities as forage resources for their livestock. Grazing is one of the most important disturbances which affect natural meadows and can produce changes at community level in the species richness and plant composition. With the aim of determining the floristic composition of the Andean grasslands in the Alto Bio-Bio National Reserve (37 degrees S y 70 degrees W) and its relationship with the cattle load, we studied five sites within the reserve: Cuchares Grande, Cajon Chileno, Tralilhue, Cuchares Chico and Mancha de Pinos. In each site, we sampled 20 random plots recording all the species and their relative cover. We recorded a total of 89 species of vascular plants. Taxonomic richness is represented by two Pteridophyta and 87 Magnoliophyta species. In this last group, 25 species are Liliopsida and 62 are Magnoliopsida. All flora is distributed ill 37 families and 72 genera. Greatest families, in species number, are Asteraceae (13), Poaceae (11), Cyperaceae (6) and Rosaceae (6). About the origin, 88 species are native and only 11 are introduced, representing 88% and 12%, respectively. Life forms are represented mostly by hemicryptophytes with 53%, then cryptophytes arround 17% and finally chamaephytes (15%). Grasslands wich have greater livestock density, have a higher proportion of introduced species and hemicryptophytes and a greater floristic similarity between them, while those with lower livestock densities have a higher native species proportion. These results suggest that cattle use could have a significant impact in the floristic composition of Andean grasslands. Even though, the low proportion of introduced species found, the high percentage of hemicryptophytes indicates an intermediate level of disturbance.