Pool boiling experiments with non-azeotropic water-ethanol mixtures were conducted under 10-second microgravity conditions available from a drop shaft facility with a 490 m free fall. Comparing with the terrestrial condition, the boiling heat transfer was enhanced under microgravity. The observation from the back side of a transparent glass plate heater suggests that the enhancement could be ascribed to the Marangoni flow induced by an ethanol concentration gradient due to preferential evaporation of ethanol along the surface of enlarged vapor bubbles detached from, but still kept close to, the heater surface under microgravity.