As is well known, ABA is synthesized inleaf tissue and is transported via the phloem to filling seed (Setteret al., 1981). The present study found that with lower the concentration of ABA in seed, the smaller was the seed size. This suggests a parallel relationship between seed growth and the ABA concentration in the cotyledon, although the relationship of ABA transport from the leaf to the seed and assimilate transfer is still unclear. Our experiments provide evidence for a pro motive role of ABA in photo assimilate accumulation in soybean seeds. ABA may stimulate rapid unloading of sucrose into the seed coat apoplast andmay enhance movement of sucrose into cotyledons during the seed filling stage