  The radioactive noble gas radon-222 ($\mathrm{^{222}Rn}$, or Rn) produced in
the uranium series is a crucial background source in many underground
experiments. We have estimated the adsorption property of Rn with Activated
Carbon Fibers (ACFs) in air (Air), argon (Ar), and xenon (Xe) gas. In this
study, we evaluated six ACFs, named A-7, A-10, A-15, A-20, A-25, and S-25,
provided from UNITIKA Ltd. We measured intrinsic radioactivity of these ACF
samples, and found A-20's radioactivity of the uranium series is
$<5.5$~$\mathrm{mBq/kg}$ with $90\%$ confidence level. In Air and Ar gas, we
found ACF A-15 has the adsorption efficiency of $1/10000$ reduction at maximum
before saturation of Rn adsorption, and more than $97\%$ adsorption efficiency
after the saturation. In Xe gas, we found ACF A-20 has the best Rn adsorption
ability among tested ACFs. We also found S-25, A-25, and A-15 have similar Rn
adsorption performance.
