The optical limiting effect was numerically simulated and experimentally observed for a 25-layer thin-film Fabry-Perot microresonator by 7 ns laser pulses at 532 nm. The sample, made by vacuum evaporation and consisting of alternating Nb2O5 and SiO2 layers, has an ultranarrow line of transparency at near 532 nm within a wide spectral band of reflection. By adjusting simulated results in accordance with experimental dependencies of transmittance, reflectance, and absorbance on incident light intensity, the coefficient of optical nonlinearity of Nb2O5 was estimated at (6+1i)·10(-12) cm2/W.