The photoreduction deposition method is employed to fabricate a family of silver nanoparticle (Ag NP)-modified polyoxometalate-based metal-organic framework (NENU-5) photocatalysts, named Ag/NENU-5. The title photocatalysts, Ag/NENU-5, can be used for the photocatalytic reduction of CO2 and are observed to efficiently reduce CO2 into CO, in which the highest reduction rate is 22.28 μmol g-1 h-1, 3 times greater than that of NENU-5. Photocatalytic reduction performances of CO2 have been extremely improved after the incorporation of Ag NPs as the cocatalyst. The enhancement of the photocatalytic reduction of CO2 has been attributed to the synergistic effects of Ag NPs and NENU-5, inhibiting the charge recombination during the photocatalytic process and increasing the reaction active sites. Furthermore, the influence of Ag NPs on the photocatalytic activity has also been investigated. The experimental results clearly reveal that the size of Ag NPs could exert a main effect on the photocatalytic activity, and the reasonable size of Ag NPs is able to enhance the photocatalytic reduction activity toward CO2 significantly.