This research had lhe objective of determining the effects of nitrogen application on seed vigor and protein content of four rice cultívars grown under irrigation. The tested cultivars were EEA-406, IAS-12-9-Formosa, Bluebelle and IRGA-408, which were investigated on 30, 60, 90 and 120kg/ha of nitrogen, applied on four periods: on planting (period l); 1/3 on planting and 2/3 on the phase of differentiation of the flower primordium (period 2); immediately before flooding (period 3); five days after flooding (period 4). Seed quality was evaluated by the accelerated aging test (vigor) and protein content determination. A randomized complete block factorial design was utilized. Planting was carried out on November 19, 1976, in Pelotas, Rio Grande do Sul. Seed vigor determined by the accelerated aging test, was not affected neither by the dosis nor by the periods of nitrogen application. It was also observed that the different dosis of nitrogen did not cause any increase in seed protein content. Seed of the IAS-12-9-Formosa cultivar showed the lowest vigor, as determined by the accelerated aging test.