Optical data in the Johnson's BV and Cousins' R bands are presented for eight X-ray selected BL Lacertae objects that have recently been pointed by the Satellite per Astronomia X `Beppo'(BeppoSAX). The observations were done with the 1.05m telescope of the Torino Astronomical Observatory and the observational periods include, or are close to, the satellite pointings. These data provide optical information on sources that have been rarely observed in the optical band. Moreover, they can be compared to the X-ray ones for a better understanding of the emission properties of these objects. Variability on short time scales (a few days) was found for MS 0317.0+1834, 1ES 0347-121, and MS 0737.9+7441. For a description of the (RI)c photometric system, see e.g. the General Catalog of Photometric Data <GCPD/54>