To be observed by Hipparcos, the position of each object has to be known with an accuracy of 1 arcsecond and its magnitude with an accuracy of 0.5 mag. Therefore, the orbital elements of the 48 selected minor planets of the Hipparcos mission, have been improved in order to extrapolate their ephemerides with the accuracy required. Updated ephemerides are given here for the year 1993 referred to the two reference frames: J2000 and 1950.0. The orbital elements which have been used to compute these ephemerides are also given.