In order to determine the effects of N on quality of lettuce seed, an experiment using 4 repplications and 4 treatments (0, 80, 160 and 320 gN/m²) was carried on. It was concluded that N fertilization did no affect seed production, but affected seed size (weight) and vigor. The size of plants at transplanting time was correlated to vigor and size of seed. The field tests are a complement to lab tests, providing better conditions to evaluate seed quality.