(K,Na)NbO3 (KNN) based ceramics, as competitive lead-free counterparts, have attracted substantial attentions because of their high piezoelectric response.In this work, KNN based epitaxial thin films were synthesized by a sol-gel method.In-situ domain structure and phase transition in Li-doped KNN epitaxial thin films has been studied during heating and cooling cycles from room temperature to 190 ℃ by means ofpiezoresponse force microscopy.