A series of ferroelectric poly(vinylidene fluoride-co-chlorotrifluoroethylene) films with different crystallite sizes have been obtained by varying the film processing conditions. The impact of the crystallite size on the dipole switching and the electric energy density has been systematically studied by the electric displacement-electric field hysteresis loop measurements. The films with smaller crystallite sizes display larger polarizability, as evidenced by higher maximum polarization and lower dipole switching field in the charging process. Small crystals also facilitate fast dipole depolarization during the discharging process. Consequently, superior released energy densities have been achieved in the films containing small sizes of the ferroelectric crystallite domains. On the other hand, large crystallite sizes are beneficial for the dielectric breakdown strength and the Weibull distribution of the breakdown field of the films. This study sheds new fundamental light on the optimization of the crystal structures of the ferroelectric polymers for high electric energy storage applications. (C) 2012 Elsevier Ltd. All rights reserved.