Priming is one of the several physiological methods used to increase the performance of seeds. To evaluate the effects of priming, seeds of Urochloa brizantha cv. Xaraes were primed under different osmotic potentials (ys = 0.0; -0.5; -1.0 and -1.5 MPa) and temperatures (15 and 25°C) for 24, 48, 96 and 144 h. The germination percentage and germination speed index were evaluated, in a completely randomized design with four replications. It was verified that priming increases percentage and germination speed index of U. brizantha cv. Xaraes seeds cultivar, and these should be primed in water at 25°C (ys = 0,0 MPa) for 85 h. Key words: Brachiaria grass, germination, forage seeds.