The phase transition dynamics of Ge2Sb2Te5 thin films induced by single nanosecond laser pulses were studied by transient optical reflectivity and electrical resistance measurements with nanosecond resolution. It was found that the real-time responses of optical and electrical signals were different under the same pumping condition. It needs much little time to reach equilibrium state for electrical resistance than optical reflectivity. The dependence of crystallization time determined respectively by optical and electrical evolution curve on laser pulse fluence was compared and analyzed. A 2-dimensional percolation model was used to explain the differences between electrical and optical transient responses. (C) 2011 Elsevier B.V. All rights reserved.