GAIA will likely be a real milestone for asteroid science. Its unprecedented astrometric accuracy can be exploited to compute orbits better than those obtained by using the whole set of available astrometric observations carried out from ground during the last 100 years. GAIA will make it possible to measure asteroid masses through the measurement of the tiny displacements caused by asteroid mutual encounters. This will be a major breakthrough for physical studies of minor planets. Moreover, sizes will be also directly measured for a big sample of more than 1000 objects. From masses and sizes, estimates of the average densities will be also obtained. The spectrophotometric capability of GAIA will be used for purposes of taxonomic classification, with important implications for surface mineralogical characterization. Finally, GAIA will be an ideal platform to detect near-Earth asteroids having orbits interior to that of the Earth.