The spectrum averaged cross sections of the ⁹³Nb(n,n′)^93mNb reaction in two standard fission neutron spectra have been measured by the activation method. The two standard spectra were the 252Cf spontaneous fission neutron spectrum and the thermal neutron induced fission neutron spectrum of 235U. Effective free-field neutron fluences were established by neutron source strength calibration against the National Standard Ra-Be source, fluence transfer from intermediate standard sources, and Monte Carlo scattering corrections. Activity measurements were performed by X-ray counting using a variety of Ge and Si(Li) spectrometers with sources prepared by deposition of niobium fluoride on analytical paper discs. The recommended values of the spectrum averaged cross sections for the ²⁵²Cf and ²³⁵U fission neutron spectra are, respectively, 150.6 mb ± 3% and 146.4 mb ± 3%.