We report magnetostriction measurements in polycrystalline Ca 2 FeReO 6 magnetic double perovskite up to 20T and in the temperature range 4.2–250K. This compound shows a high Curie temperature (TC=523K) and a structural transition at low temperatures (TS=110K). By combining magnetostriction measurements parallel and perpendicular to the magnetic field, we evaluate the anisotropic (λ t ) and volume magnetostriction (ω). The λ t at room temperature is large and reaches below T S the giant value of ≈0.1% at 15T. Below T S , the ω is also found to be large: ≈0.05% at 15T at 5K. These results are interpreted within a scenario where the Re orbital state plays a crucial role in the ground state. The observed effect could open a new way to observe giant magnetostriction effects in transition-metal-based magnetic oxides through suitable tuning of the orbital effects in the transition metals.