Pastures dominated by native and naturalized species account for a large portion of the total grassland area in southern Chile. However, information on these ecosystems is scarce, particularly with respect to the seeds of the species that compose them. The objective of this study was to evaluate the physical and germinative characteristics of Bromus valdivianus Phil., Paspalum dasypleurum Kunza ex Desv., Holcus lanatus L., Agrostis capillaris L. y Arrhenaterum elatius L. spp. bulbosus (Wild), collected from two geographical areas of southern Chile and classified into two contrasting sizes. The areas evaluated were the foothills (Coastal Mountain Range) of the commune of La Unión and the foothills (Los Andes Mountain Range) of the commune of Lago Ranco. Seed germination percentage, germination rate, diameter, length, and 1000 seed weight were determined. Subsequently, germination vigor was determined by measuring leaf length, aerial weight, root weight and total weight of the species. In addition, a pot experiment was conducted under controlled conditions of temperature, light and humidity to determine establishment vigor, measuring the same parameters as for germination vigor. The data were analyzed under a completely randomized nested design. Bromus valdivianus Phil. was the species that showed the best performance in all the evaluated variables (P < 0.05). In terms of locality of origin, Lago Ranco recorded larger seeds, while La Unión presented better germination. In terms of size, large seeds proved to be more vigorous and had better germination performance. It was concluded that germination percentage and rate as well as vigor of germination and establishment vary between seed size and locality of origin within the same species.