Rubber three seeds utilized in Brazil present some chronic problems related to their quality, possibly because these seeds are not submitted to any kind of seed processing. A certain percentage of these seeds have a low specific weight which probably adds to their poor performance in germination and vigor. This paper reports an attempt to process rubber tree seeds with the aid of the gravity separator. The work was conducted at the Department of Agriculture and Horticulture at ESALQ/USP, Piracicaba, SP. The seeds used in this trial were treated with fungicide with the purpose of evaluating its effect on seed physiological quality. The gravity separator divided the lot of seeds in two weight classes. No difference was detected in the germmation and vigor tests between the two classes of weight. The fungicide used (Benomil) was found to be toxic to the germination and vigor.