We have investigated the environment of the giant radio galaxy NGC 315 with its associated group of galaxies selected by their spectroscopic redshifts. Observations were made with the 2.16-m optical telescope at Xinglong Station of the National Astronomical Observatories of China. In addition to 25 galaxies near NGC 315 with published redshifts, we have successfully determined 21 new redshifts of candidates, five of which are previously unknown members of the NGC 315 galaxy group. We examine and discuss the spatial structure and kinematics of this group (which is part of the Perseus–Pisces filament). Nearly 40 per cent of its members are concentrated near NGC 315, close to the emission from its brighter radio jet. The X-ray luminosity implied by the optical velocity dispersion is higher than that derived empirically from observations of other groups, suggesting that X-ray-emitting gas within the NGC 315 group has a low density. This may be one reason for the size of the radio source.