Four ionic liquids with formula of [Rdmaz][N(CN)₂], R=ethyl(e), n-butyl(b), n-hexyl(C₆) and n-octyl(C₈), were synthesized through a metathesis reaction of quaternized N, N-dimethyl-2-azidoethylamine (DMAZ) with different alkyl chain length with silver dicyanamide. The density, dynamic viscosity and thermal properties of these ionic liquids were measured over a wide temperature range. The effect of the alkyl chain length was discussed on the physicochemical properties. Density decreases while dynamic viscosity and molar heat capacity increase with increasing number of carbon atoms in the alkyl chain. The density shows a linear decrease with temperature, and the dynamic viscosity decreases with temperature following the Vogel-Fulcher-Tamman (VFT) equation. The molar heat capacity (C_{p, m}) increases with temperature following the equation C_{p, m}=a+bT+cT². No melting points were found for these four ionic liquids except for a glass transition temperature (T_g). The T_g values were -102 ℃ for [edmaz][N(CN)₂], -92 ℃ for [bdmaz][N(CN)₂], -89 ℃ for [C₆dmaz][N(CN)₂], and -91 ℃ for [C₈dmaz][N(CN)₂]. The decomposition temperatures of these four ionic liquids range from 241 ℃ to 242 ℃, independent of the alkyl chain length.