Experiments on subcooled pool boiling of water were performed under microgravity (0.01~0.04 of normal gravity ge) given during parabolic flight of a business-jet. A thin stainless steel plate was used as heating surface. It was electrically heated and burned out under the microgravity. The bubble behavior was observed and the burnout heat flux was measured for the subcooled liquid. Boiling bubbles stayed on the heating surface under the microgravity and the burnout heat fluxes were 200 ~ 400 percent higher than those given by the existing theories. In the ground experiment, a flat plate was placed over the horizontal heating surface to simulate the attached bubbles on the surface during boiling. The experiment was performed using the same procedure as followed under the microgravity. The same burnout heat fluxes were obtained as those given under the microgravity. But as the heating time was extended over one parabolic flight duration, the burnout heat fluxes decreased gradually and became constant values as predicted by the existing theories for the microgravity.