Heat tolerance of 20 rice germplasms introduced from USDA were evaluated at seedling stage based on relative survival rate of seedling. The length of dehiscence at the basal part of thecae (BDL) which significant related with heat resistance on heading time and the length of anther (AL) were measured during flowering. After treated with heat and then recovered for 7 days, the relative survival rate of seedling of those germplasms was from 83.23 to 100%. When they recovered for 10 days after heat treatment, the relative survival rate of seedling was from 68.18 ~ 100%. N22, AD-1140, IR9403-3-1-1 and IR4427-51-6-3 showed high heat tolerance at seedling stage. BDL and AL of germplasms were ranged from 234.9 to 559.0 um and 1570.0 to 2351.7 um, respectively. Significant correlation between BDL and relative survival rate of seedling was found. The results indicated that the BDL also might be considered as the index of heat tolerance during seedling stage and deeply research is necessary in the future.