Stabilization of protein structure by solvent components, also refered as co-solvents and osmolytes, is a simple and effective strategy for preserving or enhance protein conformational stability under adverse thermal conditions. The effect of trehalose (0.5M) on the thermal stability of cutinase in the alkaline pH range was studied. The thermal unfolding induced by increasing temperature was analysed in the absence and in the presence of trehalose according to a two-state model (only the folded and unfolded states of cutinase are present). Trehalose stabilizes the reversible unfolding. The mid-point temperature of the unfolding transition (Tm) increases 3.5 ºC and 2.6 ºC at pH 9.2 and 10.6, respectively. The unfolding occurs at higher temperatures for pH 9.2 and a refolding yield of around 80% was obtained upon cooling. Therefore this pH value was chosen to study the irreversible inactivation (long-term stability) of cutinase. Temperatures in the transition range from folded to unfolded state were selected and the rate constants of irreversible inactivation determined. Inactivation follows first-order kinetics and trehalose reduces the observed rate constant of inactivation, indicating also a stabilizing effect on the irreversible inactivation step of thermal denaturation. However, if the contribution of reversible unfolding on the irreversible inactivation of cutinase is taken into account, we concluded that the stabilizing effect of trehalose on the irreversible inactivation is apparent. This statment is further suported by comparing the activation energy of the irreversible inactivation in the absence and in the presence of trehalose calculated from Arrhenius plot. The activation energy is similar, slightly larger, in the absence (14.9 Kcal/mol) than in the presence of trehalose (8.0 Kcal/mol). In fact, trehalose stabilizes only the reversible step thermal denaturation of cutinase.