We carried out observations of 16 asteroids with different ISO instruments (PHT-P PHT-S and SWS) obtaining low resolution spectra up to 12 micron high resolution spectra up to 45 micron and spectrophotometric data up to 60 micron. The aim of these observations was to investigate the physical properties of the surface of these bodies and to improve our understanding on the processes which governed their formation and evolution. We interpreted the obtained data in terms of asteroid surface composition comparing the observed spectra with laboratory reflectance spectra of selected mineral mineral mixture and meteorite particulates of different grain sizes. The characterization of the material on the asteroid surfaces (presence abundance and/or composition of minerals or chemical species) was based on the interpretation of observable diagnostic spectroscopic properties. The obtained results will be presented and discussed.