We perform Molecular Dynamics simulations to investigate the strength properties of particulate reinforced nanocomposites. For a fixed reinforcement volume fraction, the effective strength increases as the inclusion size decreases. We further develop a kinematic limit analysis approach, which delivers theoretical estimates of the effective strength. The model is first assessed in the absence of size effects by comparison with data from available literature. An extension to nanocomposites is then proposed, accounting for the presence of surface stresses at the matrix/inclusion interface. Numerical data are used to calibrate the interfacial strength, which is found to be a size-dependent property.