The 4T1 tumor model closely approximates the characteristics of human breast cancer and is widely used in laboratory research. Knowledge of the optical parameters of the tumor is important for choosing the correct parameters for laser treatment. In this paper, optical properties and refraction indices of breast tissue in healthy mice and 4T1-model breast tumor have been measured. Using these measurements, absorption coefficient and reduced scattering coefficient have been reconstructed. A significant decrease in both the scattering and refractive index of tumor tissue has been observed. The change in tissue morphology has induced the change in the slope of the scattering spectrum. Thus, the light penetration depth into tumor has increased by almost 1.5-2 times in the NIR “optical windows.” Raman spectra have shown lower lipid content and higher protein content in tumor. The results may be useful for modeling the distribution of laser radiation in healthy tissues and cancers.