We report the effect of cyclodextrin (CD) cavity size on the photovoltaic performance of dye-sensitized solar cells (DSSCs) containing inclusion complexes of tris(2,2′-bipyridyl)ruthenium(II) ([Ru(bpy)3]^2  +) in various CDs ([Ru(bpy)3]^2  +  /  CD). The incident photon-to-current conversion efficiency (IPCE) of the [Ru(bpy)3]^2  +-containing DSSC at 460 nm was calculated to be 8.1%, and this value was enhanced by the formation of [Ru(bpy)3]^2  +  /  CD. The IPCE values of [Ru(bpy)3]^2  +  /  α-CD-containing, [Ru(bpy)3]^2  +  /  β-CD-containing, and [Ru(bpy)3]^2  +  /  γ-CD-containing DSSCs were 8.8%, 8.9%, and 11.2%, respectively. It was concluded that the difference of IPCE values of [Ru(bpy)3]^2  +  /  CD-containing DSSCs were caused by the CD cavity size, which affected the host–guest interaction between [Ru(bpy)3]^2  + and the CD. These findings indicated that the cavity size of γ-CD is suitable to promote the photovoltaic conversion of DSSCs containing an unanchored photosensitizing dye with nonplanar molecular structure such as ruthenium(II) polypyridine and diimine copper(I) complexes.