Olive tree cultivation generates a great amount of biomass residues which have no industrial application. Pruning residues are usually grindered or burnt on fields, causing economical costs and environmental concerns. An alternative issue for these renewable sugar-containing feedstocks may be the conversion into fuel ethanol by hydrolysis and fermentation. As a first step in the bioconversion process, the acid hydrolysis of olive tree pruning is studied and a mathematical model predicting both fiber content and sugar release as a function of operation variables is proposed. Sulphuric acid concentration in the range 0-32% (w/w), process temperature between 60 and 90 degrees C and hydrolysis time from 0 to 240 min were used as hydrolysis conditions. The process was modelled by first-order reaction kinetics. The apparent kinetic constant relating acid concentration to fiber hydrolysis and sugar release shows a potential dependence; on the other hand, an Arrhenius-type equation has enabled the evaluation of activation energy values of 26.4 and 25.9 kJ/mol for fiber hydrolysis and sugar generation, respectively. (C) 2009 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.