The nanoscale properties of materials can have a great influence on their macroscopic behavior; for instance, the generation and accumulation of defects at the nanoscale, such as point defects, porosity, and interfaces, can change their thermal properties. In this work, we study the role of an interface in the thermal conductivity between two nanoparticles without any external load. We consider a system subjected to a temperature gradient perpendicular to the contact surface and study the thermal conductivity, thermal conductance, thermal resistance, and contact resistance vs nanoparticle size. The thermal resistance at the interface increases linearly with nanoparticles' contact radius ac. A model based on the contact area between two nanoparticles allows us to reasonably explain the obtained numerical results for the thermal conductivity, leading to a net decrease in effective conductivity as the nanoparticle size increases, reasonably well described by a (a(c)/R) dependence. Simulated thermal conductance was found to be proportional to (a(c)/R).