<p>The accurate measurement of radioxenon isotopes is crucial to the operation of nuclear facilities and the implementation of the Comprehensive Nuclear-Test-Ban Treaty. In this work, two methods: γ spectrometry and length-compensation proportional counting method are employed to measure the activity concentrations of ¹³³Xe and ^133mXe mixed gases generated by the ¹³²Xe (n, γ) ¹³³Xe reaction. The detection efficiency of the γ spectrometer is obtained via Monte Carlo simulation, while the proportional counters distinguish counting contributions by means of the isotope activity ratio measured by the γ spectrometer. After correction to the reference time as well as standard temperature and pressure (101.325 kPa, 273 K). The activity concentration results measured by the two methods show good consistency, with a relative deviation of 0.76% for both ¹³³Xe and ^133mXe activity concentrations.</p>