The calculated results show that the developed model can give much accurate predictions for yield strength of nanocomposites by proper thickness and strength of interphase, while the yield strength is under-predicted by disregarding of interphase. The developed model demonstrates that the yield strength improves by reduction in nanoparticle size and increment in interphase thickness. Also, the detrimental effect of weak interfacial adhesion between polymer matrix and nanoparticles is revealed.