The exergetic analysis is a tool that has been used successfully in many studies aiming a more rational energy use reducing the cost of the processes. With this analysis it is possible to perform an evaluation of the overall process, locating and quantifying the degradation of exergy. In this context, the present work aimed the exergetic analysis of the refrigeration cycles in ethylene and propylene production process, calculating the loss of exergy, in order to propose changes in the operational variables of the cycles used, trying to reduce the rate of destroyed exergy in the process. The commercial simulator Hysys((c)) (version 3.2) was used to obtain thermodynamic properties of the process streams and to perform mass and energy balances. The application of new operational conditions in these cycles resulted in a reduction of about 13% of the losses of exergy for the refrigeration system of the process. (C) 2009 Elsevier Ltd. All rights reserved.