Polysiloxane derivatives having quaternized imidazolium moieties with different length of alkyl chains ([HPIm n ]Cl) (n is the number of methylene group) were prepared via quaternization reaction of poly(3-chloropropylmethylsiloxane) (P1) with 1-alkylimidazole derivatives (Im ns). [HPIm n ]Cls were obtained with high quaternization ratio from 95 to 100 mol%. The glass transition temperatures (T (g)s) of a series of [HPIm n ]Cls were lowered with increase in the length of alkyl chain in the case of the number of methylene group from 1 to 6; however, those were a little raised when the number of methylene group was 7 and 8 plausibly owing to the effects of the van der Waals interactions among long alkyl chains. [HPIm n ]Cls were dissolved in high polar solvents such as methanol, dimethyl sulfoxide, N,N-dimethylformamide and water. Also, the increase in the length of alkyl chains in [HPIm n ]Cls improved the solubility in low polar organic solvents such as chloroform and dichloromethane.