1. Motivation The knowledge of tissue optical properties is necessary for the development of the novel optical technologies of photodynamic and photothermal therapy, optical tomography, optical biopsy, etc. Numerous investigations related to determination of tissue optical properties are available however the optical properties of many tissues have not been studied in a wide wavelength range. Goal of the study is to investigate of optical properties of human nasal polyps in the wavelength range from 350 to 2500 nm Materials and methods  For this study twenty samples of human nasal polyps have been used. The samples were kept in saline during 48 hours at temperature 4-5°C until spectrophotometric measurements. The size of the samples were approximately 15×15 mm, the average thickness was 1.0±0.5 mm. For mechanical support, the tissue samples have been sandwiched between two glass slides  Measurement of the total reflectance, total and collimated transmittance have been performed using a commercially available spectrophotometer LAMBDA 950 (PerkinElmer, USA) in the spectral range 300-2500 nm  All measurements were performed at room temperature (about 20°C)  Inverse Monte Carlo technique has been used for processing the experimentally measured spectra of the tissue samples  Experimental setup Inverse Monte Carlo (IMC) Results A B C D E F Fig.3. The typical spectra of sample of human nasal polyp. R t is total reflectance; T t is total transmittance and T c is collimated transmittance (A); the wavelength dependence of penetration depth (B), the absorption spectrum (C), the wavelength dependence of scattering anisotropy factor (D), the scattering coefficient spectrum (E), and the reduced scattering coefficient spectrum (F) of human nasal polyps. IS, IMC, data averaged for 20 samples. Summary  The analysis of the results has shown that investigated spectra depend on scattering coefficient of collagen fibers and absorption bands of interstitial matrix water. The absorption bands of oxyhemoglobin at the wavelengths 415, 540 and 570 nm are well seen  Our results can be used for the development of new methods and optimization of the existing ones of therapy of rhinologic diseases Optical properties of the human nasal polyps in the spectral range from 300 to 2500 nm Ekaterina A. Kolesnikova 1, Aliya A. Muldasheva 2, Julia P. Ireneva 2, Darya N. Zmeeva 1, Alexey N. Bashkatov 1, Elina A. Genina 1, Vyacheslav I. Kochubey 1, Anatoly B. Knyazev 2, Valery V. Tuchin 1 1-Saratov State University, 2-Saratov State Medical University Saratov State University Department of Optics & Biophotonics Fig.1. The geometry of the measurements in A) transmittance mode, B) reflectance mode. 1 ‑ the incident beam (diameter 1-4 mm); 2 ‑ the tissue sample; 3 ‑ the entrance port (square 25  16 mm); 4 ‑ the transmitted (or diffuse reflected) radiation; 5 ‑ the integrating sphere (IS) (inner diameter is 150 mm); 6 ‑ the exit port (diameter 28 mm) Fig.2. The geometry of the collimated transmittance measurements. Diameter of the incident beam is 2 mm. The computer program package for determination of absorption and scattering tissue properties has been developed. This inverse Monte Carlo method based on the solution of direct problem by Monte Carlo simulation and minimization of the target function with the boundary condition