In this paper, some models for yield strength of polymer nanocomposites are developed to determine the properties of interphase and agglomerated nanoparticles. In this regard, "B-agg" parameter is defined assuming the agglomerates size (D-agg) and interphase properties. Additionally, the influences of "B-agg" and "D-agg" on the thickness and strength of interphase are evaluated by the developed equations. The agglomeration of nanoparticles causes contradictory effects on interphase properties in samples with different levels of interfacial bonding. Also, "B-agg" more depends to interphase properties compared to "D-agg". It is found that upon increasing in "B-agg" and "D-agg", the strength of interphase improves and reaches the most level at the highest values of "B-agg" and "D-agg". Therefore, controlling the levels of "B-agg" and "D-agg" is crucial to obtain a strong interphase. (C) 2016 Published by Elsevier Inc.