Red clover (Trifolium pratense L.) was grown for seed production after the seeding year on two different types of soils, in the same climatic area. An important difference in yield which was often related to cultivar and sometimes to year was observed between the two soils — the light soil, Saint-André gravelly loam, produced more seed than the heavy Kamouraska clay. Seed yield differed between cultivars with Florex and Arlington producing the most. On an annual basis, the thousand-grain weight was higher on Kamouraska than on Saint-André. The percent germination was not influenced by soil type and cultivar but variation between years was observed. The production of heads per plant was higher on Saint-André. The number of seeds produced per plant and per head was, as for yield, higher on Saint-André than Kamouraska. The influence of cultivars and years was not always visible on these last parameters. Therefore these results demonstrate that generally the success of red clover seed production depends not only on cultivar and climatic conditions, but that within the same climatic area the type of soil is a major factor. Key words: Red clover, seed production, soil effect, year of harvest, cultivar, yield components