This work examined the mass transfer efficiency of a rotating packed bed with various radii of the packed bed. Experimental results showed that k(L)a increased with decreasing volume of the packed bed. This may contribute to the significant end effects as the volume of the packed bed is reduced. A correlation which takes end effects into consideration for kLa in a rotating packed bed was proposed and is valid for different sizes of the rotating packed bed and for viscous Newtonian and non-Newtonian liquid systems. In addition, it was also found that the correlation could reasonably estimate most of the kLa data in the Higee literature.