The conversion of diluted CO2into tunable syngas via photocatalysis is critical for implementing CO2reduction practically, although the efficiency remains low. Herein, we report the use of graphene-modified transition metal hydroxides, namely, NiXCo1–X-GR, for the conversion of diluted CO2into syngas with adjustable CO/H2ratios, utilizing Ru dyes as photosensitizers. The Ni(OH)2-GR cocatalyst can generate 12526 μmol g–1h–1of CO and 844 μmol g–1h–1of H2, while the Co(OH)2-GR sample presents a generation rate of 2953 μmol g–1h–1for CO and 10027 μmol g–1h–1for H2. Notably, by simply altering the addition amounts of nickel and cobalt in the transition metal composite, the CO/H2ratios in syngas can be easily regulated from 18:1 to 1:4. Experimental characterization of composites and DFT calculations suggest that the differing adsorption affinities of CO2and H2O over Ni(OH)2-GR and Co(OH)2-GR play a significant role in determining the selectivity of CO and H2products, ultimately affecting the CO/H2ratios in syngas. Overall, these findings demonstrate the potential of graphene-modified transition metal hydroxides as efficient photocatalysts for CO2reduction and syngas production.