Liquid desiccant dehumidification system, which presents great potential for energy saving in HVAC industry, has drawn much attention in recent years. Various dehumidifiers have been proposed for achieving the better performance and are used to be evaluated by the indicator: dehumidification effectiveness. However, this widely-used indicator is found varying significantly with the operational conditions and cannot distinguish the inherent mass transfer capability of dehumidifiers from the influence of the properties of airstream and desiccant. In view of this, this paper presents a novel concept named dehumidification perfectness, based on the conversion laws of mass and energy, for realizing the impartial evaluation of the inherent mass transfer capability of dehumidifiers, getting rid of the influence from the airstream and desiccant solution. Experimental data from the open literatures was employed to validate the concept and its affecting factors were then discussed. It was found that higher degree of dehumidification perfectness was obtained with bigger/longer effective liquid gas contact area/time provided by the dehumidifier. Furthermore, with different properties of various dehumidifiers, such as the surface area densities of packing, their dehumidification perfectness was varying significantly. The concept developed here demonstrates promising potentials for comparing, predicting and improving the performance of various dehumidifiers. (C) 2015 Elsevier Ltd. All rights reserved.