A highly accurate and precise technique for measurement of the 93Nb(n,n')93mNb reaction rate was established for the material surveillance tests, etc. in fast reactors. The self-absorption effect on the measurement of the characteristic X-rays emitted by 93mNb was decreased by the dissolution and evaporation to dryness of niobium dosimeter. A highly precise count of the number of 93Nb atoms was obtained by measuring the niobium solution concentration using inductively coupled plasma mass spectrometry. X-rays of 93mNb were measured accurately by means of comparing the X-ray intensity of irradiated niobium solution with that of the solution in which stable 93Nb was added. The difference between both intensities indicates the effect of 182Ta, which is generated from an impurity tantalum, and the intensity of X-rays from 93mNb was evaluated. Measurement error of the 93Nb(n,n')93mNb reaction rate was reduced to be less than 4％, which was equivalent to the other reaction rate errors of dosimeters used for Joyo dosimetry. In addition, an advanced technique using Resonance Ionization Mass Spectrometry was proposed for the precise measurement of 93mNb yield, and 93mNb will be resonance-ionized selectively by discriminating the hyperfine splitting of the atomic energy levels between 93Nb and 93mNb at high resolution.