Photocatalytic systems for CO₂ reduction using a Ru(II) tris-diimine complex (Ru) as a photosensitiser and dinuclear Re(I) diimine tricarbonyl complexes (Re(n)Re), in which diimine ligands are connected by alkyl chains of various lengths (–C_nH_2n–: n = 2, 3, 4, 6, 14), as catalysts were investigated. The photocatalytic systems using Re(n)Re exhibited improved durability compared with that using the corresponding mononuclear Re(I) complex (Re); moreover, among the Re(n)Re, shorter alkyl chains in the bridging ligands induced greater durability. We found that the durability of the photocatalytic system depended on the decomposition speed of Ru, which could be suppressed using Re(n)Re with shorter alkyl chains.