In the present study, a novel phosphonium-based Dicationic Ionic Liquids (DCILs) were synthesized and characterized using 'H NMR and elemental analysis. Physiochemical properties such as density and viscosity are measured and reported for a temperature range of 293.15 to 353.15 K while the refractive index was measured in the range of 293.15 to 333.15 K. The start and decomposition temperatures are determined at heating rate 10°C min-1. The influence of the spacer alkyl chain on these properties is discussed. The results show that the new DCILs possess lower density higher thermal stability and higher viscosity compare to monocationic ionic liquids. © 2011 Asian Network for Scientific Information.