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This paper presents an experimental study on the dehumidification performance of a finned-tube internally cooled contactor as compared to that of an adiabatic contactor in liquid desiccant air conditioning systems with ionic liquid. The contactor is the most significant component in liquid desiccant systems; it is the component responsible for the dehumidification and regeneration processes. When air and absorptive solution are in contact in the contactor, absorption/desorption of the solution occurs due to the difference in vapor pressure. This results to the transfer of heat and mass between the air and solution. Conventionally, adiabatic contactors, which only have air and solution interaction are being used for the dehumidification/regeneration process of liquid desiccant systems. On the contrary, internally cooled contactors are being suggested as these have the possibility of realizing a more efficient dehumidification process. This is possible as internally cooled contactors can maintain the dehumidification ability of the absorptive solution by utilizing cooling water as a third fluid in the contactor for removing the heat of absorption. In other words, internally cooled contactors have the possibility of reducing the circulating solution mass flux and, hence, the power consumption of the solution pumps. In this research, the dehumidification ability of a finned-tube internally cooled contactor is experimentally studied. In order to increase the heat transfer ability of the cooling water, aluminium, which has a high thermal conductivity, is used as the contactor material. Although Lithium Chloride solution is a conventional absorptive solution, it corrodes aluminum; therefore, ionic liquid is used as the absorptive solution in this experiment since it does not corrode aluminum. Research on this new combination of contactor and absorptive solution is not extensively done at present; this research provides new and valuable information for future research. Moreover, the results were compared with that of an adiabatic contactor in order to analyze the difference in dehumidification ability between the two of contactors. As a result, outlet air dew point temperatures lower than the cooling water temperature were achieved, which emphasize the advantage of liquid desiccant air conditioning system to conventional vapor compression air conditioning systems. Furthermore, the outlet air dew point temperatures of the internally cooled contactor were lower than that of adiabatic contactor for low mass fluxes, and converged at higher solution mass flux. This suggests the significant effect of the cooling water to the dehumidification ability of the absorptive solution. Experimental data of the dehumidification ability of this new combination of aluminum finned-tube contactor and ionic liquid solution are promising for further research about the structure of contactors. These results provide significant information for the improvement in the design of liquid desiccant air conditioning systems.