The de Haas–van Alphen (dHvA) effect in the heavy fermion system CePd2Si2 was studied by magnetic torque measurements in magnetic fields up to 28 T at low temperature. A clear magnetic torque anomaly observed at Bm∼10T applied along the crystallographic a axis indicates a metamagnetic transition. The transition also manifests itself by a sharp drop of the magnetoresistance at low temperature. The dHvA oscillations observed above the transition reveal six different frequencies in the basal plane with the corresponding effective masses from 6me to 23me. Comparison of the angular dependence of the dHvA frequencies with the theoretical band-structure calculations implies that the 4f electrons are itinerant rather than localized inside a magnetically ordered state. One frequency is split into two close satellites, which most likely originate from the up and down spin bands, whose effective masses differ by a factor of 2. The spin splitting gives rise to an apparent anomalous field dependence of the effective mass obtained from the experiment.