The optical properties of the ion-implanted and annealed silicon wafer in visible spectral range are close to the single crystalline silicon due to the annealing-induced recrystallization, resulting in the unavailability of normal visible spectroscopic ellipsometry （SE） measurements. In this study, the SE measurements are performed in infrared range （2—20 μm） to characterize the implanted and annealed wafers. An optical model based on the classical Drude free-carrier absorption equation is developed, with which the impurity concentration profile, resistivity, mobility of the carriers, and the dispersion relations of the implanted layer are determined. The relationships between these parameters and the implantation dose are also analyzed. The results suggest that the infrared SE is an effective method to characterize the annealed silicon wafers. Longer wavelength should be used to distinguish lower impurity concentration.