Stacking thin graphene layers into three-dimensional (3D) microscopic structure named graphene nanoplatelets (GNPs) could render much lower thermal conductivity (κ) compared with single-layer graphene with ultrahigh κ of around 5000 W·m-1·K-1. In this study, decorating GNP surface with nanoparticles (NPs) is proposed to be an effective approach to further push down the lower limit value of κ for GNPs. By introducing six metallic and non-metallic NPs, i.e., Au, Ag, Cu, Fe, Al2O3 and SiO2 NPs onto the GNP surface, we experimentally corroborate that the κ values of GNP stacking powders approaches to 0.07 W·m-1·K-1, which is 105 magnitudes lower than that of ideal 2D graphene materials. This remarkable reduction could be ascribed to the greatly limited sizes of ideal 2D lattice structure (~2 μm) together with random stacking arrangement and extra phonon scattering sites due to the introduction of heterogeneous NPs. Significantly, it is demonstrated that even distribution and small diameter of NPs are beneficial to thermal transport of stacking GNPs. The progress made so far could pave way to GNP materials with tunable thermal transport performance.