Cationic Gemini surfactants, alkanediyl-α,ω-bis(dimethyldodecylammonium bromide) have been synthesized by the following method: firstly dodecyl bromide was prepared by the reaction of dodecanol with bromic acid in the presence of strong sulfuric acid. Dodecylbromide was then reacted with N,N-tetramethyl ethane diamine(or N,N-tetramethyl hexana diamine) to prepare the title-compounds. Micellization of these Gemini surfactants was investigated using conductivity measurement. The results showed that the critical micelle concentration(cmc) of the Gemini surfactants has a much lower value compared with that of the corresponding “ monomer” . For a series of the Geminis with the same length(s) in the spacer chain, the cmc decreased with increasing the carbon number (m) in the alkyl chain. The aggregation number(N) of the micelle also drastically decreased with m. For the same value of m, the cmc varied slightly with s, which indicated that the electrostatic interaction between the ionic-groups of the “ monomer” has been naturally changed duo to a link between the two ionic-groups of the “ monomer” through a spacer. However, N was strongly decreased with s,which may be a reason of steric inhibition coming from the ionic-groups due to a link of spacer. With increasing temperature, micellization of the Gemini surfactants was slightly enhanced.