The aim of the study was to provide visual and quantitative evaluation of normal and tumorous brain tissue images obtained by crosspolarization optical coherence tomography (CP OCT) in comparative in vivo and ex vivo studies.Materials and Methods. The study was conducted using CP OCT -a non-damaging optical method of tissue structure imaging, which is capable of obtaining real time 3D images 2.4×2.4×1.25 mm in size within a short time of 26 s. The object of the study were normal and tumorous brain tissues of 12 experimental rats of a Wistar line: 4 -intact, 4 -with an induced malignant 101.8-glioma model and 4 -with an induced malignant C6-glioma model. In the intact rats, the cortex and the white matter were studied, in the rats with tumors -the central part of the tumor on the cortical surface, first in vivo and then ex vivo. Quantitative data evaluation of the CP OCT images involved calculation of attenuation coefficients for each tissue type.Results. A comparative qualitative image analysis of normal brain tissues and gliomas showed that the CP OCT images obtained ex vivo have the intensity and the attenuation rate (in both the initial and orthogonal polarizations) greater than those obtained in vivo. Quantitative analysis of the CP OCT images revealed significant statistical differences (p<0.02) between the attenuation coefficients from both tumors and the white matter in vivo (5. A comparison of the attenuation coefficients between the cortex and the white matter of the normal brain, as well as the white matter in the normal and malignant tissues, showed significant statistical differences both in vivo and ex vivo.Conclusion. The results of a qualitative comparative analysis of optical properties of normal and tumorous brain tissues using CP OCT allow us to conclude that the images obtained ex vivo show a full qualitative similarity with the structures observed with the intravital CP OCT study. Quantitative evaluation of CP OCT signals demonstrated a significant difference in the attenuation coefficient (p<0.005) between tumorous tissue, on the one hand, and normal white matter, on the other, both ex vivo and in vivo. However, when optical coefficients of tissues are evaluated in vivo, it is necessary to introduce adjustments based on the known differences between ex vivo and in vivo attenuation coefficients.