We have been studying the dynamic behavior of hydrogen isotopes flowing between viscous and molecular regions in an adsorbent packed-bed column, for the purpose of developing a pressure swing adsorption (PSA) process system for hydrogen isotope separation. This PSA system consists of adsorption, evacuating desorption and hydrogen replenishing processes. The kinetics in the adsorption process has been becoming to be predictable in theoretical simulation based on experimental results, but it is difficult as yet to simulate the dynamic behaviors in evaluating and replenishing processes because of the complicated geometry of passages in a packed-bed and the change of gas flow patterns between viscous and molecular regions depending on not only the pressure but also the dimension of passages. In the dynamics, the important factor should be known is the mass flow conductance in pellet packed-bed. In this work, we carried out the experiment for examining the dependence of the conductance on the diameter of particles packed in a column, since the geometrical and dimensional conditions of passages are affected by the size of packing pellets. From the experimental result and its analysis, we clarified the pressure and particle-size dependences of the conductance of hydrogen isotopes in spherical pellet packed-beds.