This paper reported the use of single-walled carbon nanotubes (SWCNTs) with terminal carboxylic acid groups as an electron-transfer bridge layer for improved photocurrent of viologen/Ru complex-based photoelectrochemical cells. The preparation of SWCNTs on tin-doped indium oxide (ITO) was prepared by spray-coating. The formation of Ru(2,2‘-bipyridine-4,4‘-dicarboxylic acid)2(NCS)2 [(RuL2(NCS)2)]/di(3-aminopropyl)viologen (DPAV)/SWCNTs/ITO was prepared by formation of acid−base complex. RuL2(NCS)2/DAPV/ITO and RuL2(NCS)2/DAPV/SWCNTs/ITO showed photocurrents of 5.6 and 10.3 nA/cm2 under A.M 1.5 condition (I = 100 mW/cm2), respectively. The photocurrents of the RuL2(NCS)2/DAPV/SWCNTs/ITO cells in which Ru complexes were attached to carbon nanotubes by only acid−base complex formation were raised to 83.9% in comparison with RuL2(NCS)2/DAPV/ITO due to retardation of recombination reaction in photoelectrochemical cells.