The aim of this work was to study the cracking of palmitic and oleic acids to reveal the role of alumina surface in the formation of deoxygenated products. Saturated palmitic acid and monounsaturated oleic acid were cracked at 650 degrees C, either in their molecular form or after preadsorption on a transition alumina surface. Cracking was performed in a micro pyrolyser, with fast heating rate, under helium flow and with "on line" products analysis (GC/MS). The alumina played an important role in the products distribution, increasing both the conversion and the deoxygenation efficiency. Oleic acid cracking in the presence of alumina produced a high content of hydrocarbons in the gasoline range (C4-C9), whereas cracking of palmitic acid produced a high content of hydrocarbons both in the kerosene range (C10-C14) and in the gasoline range.