A silver film was deposited on silicon wafer by DC unbalance magnetron sputtering system. The temperature dependence of the silver film was investigated. The spectroscopic ellipsometry (SE) with the heating of sample stage (HTC100) was employed for the in situ SE measurement under annealing cycles of the sample from room temperature to 300°C in dry nitrogen gas. The results show that the pseudo dielectric constants (<ε1>, < ε2>) of the sample varied with an annealing temperature. The real part of pseudo dielectric constant (<ε1>) of annealed Ag film was slightly changed and the imaginary part (< ε2>) was strongly increased at a photon energy below the optical band gap (3.5-4.5 eV). Furthermore, the pseudo dielectric constant of imaginary part at low energy region was changed due to the enhancement of crystallinity of Ag film at 300°C. All measured SE spectra were fitted by Drude-Lorentz optical model, the scattering time and resistivity were obtained.