The influence of seed size and origin on yield and pod and seed characteristics of peanut cultivar Tatu was evaluated in two field experiments carried out at Pindorama and Ribeirão Preto-SP, locations during the 94/95 growing season. Experiments were designed in completely randomized blocks with four replications. The treatments consisted in four screen-sized seeds of the foundation class, 18, 20, 22 and 24, and two commerciai seeds of screen 20. Little or no effect of the various treatments on yield was observed. Significant differences were obtained in pod and seed attributes, especially in relation to seed grading between the foundation and the commercial planting materials. Harvested seeds of the registered classes tended to present higher proportions of smaller (< 18 and 18 screen size) seeds then the foundation seeds. These data suggest the hypothesis that, since cultivar Tatu may contain some genetic variability for seed traits, the continued use of planting seeds of smaller sizes (a common practice among peanut growers) may have modified the frequency of seed size in some lots of this cultivar.