Growing interest in cancer radiotherapy has led to the application of nanoparticles as radiosensitizers. Here, we, for the first time, present the results of the radiosensitizing properties of silver nanoparticles (AgNPs) (possessing low toxicity towards human body) against cancer cells under neutron irradiation. Five standard cancer cultures (including glioblastoma, known for its resistance to conventional photon radiation) were used to evaluate the radiosensitizing properties of AgNPs suing MTT test, flow cytometry, and optical fluorescence microscopy. Neutron irradiation was applied in the absorbed dose of 0.5-1.5 Gy with an average neutron energy of 7.5 MeV. AgNPs increased the irradiation efficiency with the radiosensitivity enhancement ratios 1.02-2.32, for glioblastoma with ratios 1.22-1.47. It was revealed that at 1.5 Gy, AgNP-induced cytotoxicity made a significant contribution to the total observed radiosensitizer effect: on average, for five cell types, 29.8 and 96.2 % at the AgNP concentration of 0.2 and 1.6 μg/mL, respectively.