Applying the hydraulic radius model to laminar flow in a packed bed and assuming that mass transfer in the packed bed is analogous to that between a pipe surface and a stream of liquid with steady laminar velocity profile, liquid-phase mass transfer from the packed solid sphere was analyzed and an approximate solution is proposed. Further liquid-film mass transfer coefficients were measured for benzoic acid-water system. From these results, together with previous data, it was found that the proposed equation agrees with data in Re''<10, both this equation and Carberry''s equation can be applied for 10<Re''<1OO, and Carberry''s equation fits in Re''>100.