Experiments on subcooled and saturated pool boiling of ethanol are conducted on horizontal heated surfaces with micro- and nano-sized structures. The effects of structure size on bubble nucleation and departure characteristics as well as the heat transfer coefficient are discussed. It is found that microstructures can enhance bubble nucleation by significantly increasing the active nucleation site density at low heat fluxes, thus reducing the wall superheat and enhancing heat flux; while nano-structures can accelerate bubble departure by decreasing bubble departure diameter and increasing departure frequency. On the other hand, nano-structures will delay bubble mergence and prevent the vapor film from spreading at high heat fluxes during boiling crisis. (C) 2013 Elsevier Ltd. All rights reserved.