Neutron-activated 31Si is an almost pure beta emitter and is one of the short-lived radionuclides, including beta-gamma emitter 56Mn, which were created in a form of residual radioactivity in the early period after the atomic bombing of Hiroshima and Nagasaki. The features of the biological effects of internal irradiation by these radionuclides are a subject of scientific discussions and research. The publication presents data on internal radiation doses in experimental Wistar rats that were exposed to sprayed neutron-activated microparticles of 31SiO2. Doses of internal radiation could be conditionally divided into three groups according to their values. It has been found that elevated values of internal radiation doses in rats' organs/tissues as a result of exposure to sprayed 31SiO2 microparticles with initial activity of 3.2 × 107 Bq varied from 10 to 120 mGy (eyes, lungs, skin, stomach, jejunum, large intestine). The moderate dose values were in the range from 1.9 to 3.7 mGy (trachea, esophagus, ileum). The smallest doses were received by the kidney, testis, blood, cerebellum, heart, liver, cerebrum, bladder, spleen and thymus (from 0.11 to 0.94 mGy). The obtained data are important for interpreting the results of ongoing and planned biological experiments with 31SiO2 microparticles-in comparison with the previously published data on features of biological effects caused by beta-gamma emitting 56MnO2 neutron-activated microparticles.