Abstract: A novel carbon based composite counter electrode with diffusely-distributed aluminum particles was fabricated as base catalytic film of counter electrode, and the influence of the catalytic film thickness on photoelectric properties of the assembled dye-sensitized solar cells (DSC) and the function mechanism of the aluminum particles were investigated. The results show that the conversion efficiency of the assembled DSC increased firstly and then decreased with the catalytic film thickness increasing. When the thickness of catalytic film was 44 μm, the conversion efficiency reached a peak of 5.15%, the efficiency was improved by 21.5% compared to that of the optimum pure carbon counter electrode based DSC. The small size aluminum particles diffusely distributed in the composite counter electrode and acted as bridge between carbon particles, which could accelerate the electron transport of the external circuit and electrolyte reduction. As a result, thicker catalytic film possesses enhanced catalytic activity and thus counteracted the effect of the increasing resistance due to the thickening of the catalytic film. Accordingly, the conversion efficiency of DSC increased.