The waste-to-energy process consists of the combustion of some types of refuses in order to have an energetic gain. To get the most out of some types of civil or industrial refuses as alternative fuels, it is necessary to know well each characteristic of them. The aim of this work is to study the thermal behaviour of some ashes, which derive from the combustion of such refuses. It is necessary to find a technique which not only determines the melting and softening points of the ashes (parameters which influence strongly the choice of a fuel), but also is able to give information on the behaviour of the samples during the whole thermal cycle. The experimental method used in this study is the analysis with the heating microscope, which is a very helpful instrument to follow the behaviour of materials subjected to a heating cycle .