A series of the ruthenium(II) complex and viologen-containing partially quaternized poly(1-vinylimidazole)s with various degrees of quaternization (RuVQPIms) and various lengths of the alkyl side-chains [CnRuVQPIms:n = 4(butyl),8(octyl),12(dodecyl),16(hexadecyl)] have been synthesized and characterized using UV-Vis absorption and luminescence spectroscopies. The effects of quaternization and length of the alkyl side-chains on the photosensitized charge separation using these metallopolymers have been investigated in methanol, The photosensitized charge separation reaction took place through an intrapolymer process for all systems, in the cases of the RuVQPIms having a low degree of quaternization and short alkyl side-chain, the initial rate of the viologen radical formation linearly depended on the polymer concentration with two stages, while the RuVQPIm having a high degree of quaternization and long alkyl side-chain showed only one-stage dependence. Further, the rate of the second stage was larger than that of the first stage. The dependence with two stages would be caused by aggregation at a high polymer concentration through the interpolymer van der Waals interaction. The stronger interaction induced by increases in the number and length of the alkyl side-chains on the polymer backbone decreased the flexibility of the viologen residues; consequently, the enhancement of the rate in the second stage was not observed.