Diffuse reflection spectra, diffuse and collimated transmittance spectra of the mucous tissue of stomach anthrus in norm and at a low-differential form of stomach cancer are measured in 300–800 nm spectrum range. The optical coefficients of absorption (μa), scattering (μs) and anisotropy factor (g) for tissues with pathological changes have been calculated by the three-flux model and diffusion approximation methods. It has been determined that the magnitude of optical parameters grows with the development of malignant processes in stomach tissues which indicates the prevalence of forward light scattering and the increase in Mi scatter contribution to the total scattering coefficient of malignant tissues. It has also been shown that the application of two independent theories as methods of tissues' optical parameters determination (μa,μs,g) gives satisfactorily similar results.