Seven hundred and thirty varieties of soybean from different sources were evaluated for seed flooding tolerance by the seed germination test after a 4-day soaking at 25℃. The inheritance of seed flooding tolerance was also analyzed with a 6 x diallel cross. A large variation in seed flooding tolerance existed in the soybean germplasm as reflected in the germination rate which ranged from 0 to 100%. Most of the varieties tested were sensitive to seed flooding, and only 4% of the tested varieties showed a high tolerance (germination rate >90%). Seed flooding tolerance was controlled by both additive and dominance genes and a small number of effective factors and high narrow sense heritability in diallel analysis indicate that the selection for tolerance can effectively be done in early generations.