Vertically aligned graphene (VAG)/nanodiamonds (NDs) laminated composites were prepared by a series of treatments, including electrochemical exfoliation, adsorption, vacuum filtration and cold pression to study the influence of the mass percentage of NDs (0, 0.6%, 1.0%, 4.0%, 7.0%, 10.0% and 20.0%) on the thermal conductivity of the composites. The phase composition, the surface groups, the microstructure of composites were analyzed by XRD, Raman spectroscopy, FT-IR spectrometer, HRTEM and FE-SEM. The results show that the as-produced composites have a vertically aligned layer structure, and that the thermal conductivity of composites with 0.6% NDs reaches a maximum of 5.911 W/(m·K), which is 53.6% higher than that of graphene without NDs.