To study the effect of branched spacer on the property of Gemini imidazolium surfactants, Gemini imidazolium surfactants of 2,4-［bis(3-alkylimidazolium-1-yl) bromide］-1,3-propanediol (［C_n-P-C_n］Br₂, where n is the hydrocarbon chain length of 0,2 or 14) were synthesized with 2,2-dibromomethyl-1,3-propanediol as the spacer. Their surface activity and thermodynamic properties of micellization were characterized by surface tension and electrical conductivity measurements. The values of critical micelle concentration (ccmc), saturation adsorption values at the air/aqueous interface (Γmax), the area per surfactant molecule at the air/aqueous interface (Amin), the efficiency of adsorption (pC20) and surface pressure (πcmc) derived from surface tension measurement at 25 ℃ suggested that the surface activity of ［C_n-P-C_n］Br₂ was high. While Gibbs Free Energy of micellization (ΔGm) of all the surfactants derived from electrical conductivity were all negative, indicating that the formation of micelles was spontaneous.