Nanoscale domain growth dynamics of ferroelectric poly(vinylidene fluoride-co-trifluoroethylene) thin films were investigated by piezoresponse force microscopy. A 90 nm thick ferroelectric polymer thin films were fabricated on Au substrate by spin-coating method. The domain size of nanoscale dot pattern was linearly proportional to logarithmic value of the pulse width. However there was a significant asymmetry in nucleation and lateral domain growth depending on the voltage polarity, which implies the existence of the preferred polarization states. The obtained activation field indicates the nucleation-limited domain switching behaviors of ferroelectric polymer thin films.