We present a quantitative study of 180° domain wall motion in epitaxial BiFeO3 (111) films, which can be treated as a nearly ideal single-domain environment. The domains were dynamically written by applying voltage pulses and examined by the piezoresponse force microscope technique. A transition of domain growth behaviors from the activated type to the nonactivated type was observed when increasing the pulse voltages. The obtained activation field was close to the ideally thermodynamic switching field of BiFeO3. The asymmetry of activated fields showed the preference of the downward polarization in the BiFeO3 / SrRuO3 films.