Effects of surface morphology on the retention loss of ferroelectric domains of poly(vinylidenefluoride-co-trifluoroethylene) thin films were investigated using piezoresponse force microscopy. We found that the retention loss occurred by nucleation of opposite domains at the regions with morphological gradients between 0.079 and 0.146. In addition, we observed collective decreases in piezoresponse amplitude of the opposite domains after 0.8 × 106 s, although each reversed domain showed different growth rate as evidenced by different threshold time for phase reversal. These results suggest that the surface morphology has a strong influence in determining the nucleation and growth kinetics by which the retention loss occurs.