Pure Ge2Sb2Te5 thin films and Si-doped Ge2Sb2Te5 thin films were deposited by electron beam evaporation method. The property of Si-doped Ge2Sb2Te5 films are compared with that of pure Ge2Sb2Te5 films. Through in situ resistance measurement and I–V characteristic tests, an improvement of amorphous stability and an increase of crystalline resistivity are observed. The phase-separation phenomenon is observed in TEM pictures and a distinct decrease of crystal grain size in Si-doped Ge2Sb2Te5 thin film can be seen in HRTEM pictures. A blueshift and broadening of peaks after Si doping in Raman spectra are found and from absorption spectra, the broadening of crystalline optical bandgap in Si-doped Ge2Sb2Te5 thin film is proved. Finally, the behavior of doped Si atoms is proposed to explain the effect of Si doping in Ge2Sb2Te5 thin film.