Local polarization of a sol-gel-derived (Pb,La)(Zr, Ti)O3 thin film is studied from its piezoelectric response measured by using atomic force microscopy. Topographic and piezoelectric images show that the domain sizes of spontaneous polarization and grain sizes are both within the range of tens to hundreds of nanometres. Nanosized domain arrays have been written in an unpoled region to realize data storage by applying pulse voltage. The results show that the domain sizes grow exponentially when the pulse duration increases.