At the first step, this paper describes a developed model for tensile strength of interphase layers (sigma(k)) in polymer nanocomposites. The "sigma(k)" is expressed as linear, exponential and power functions of the distance between nanoparticles and polymer matrix (x(k)). Afterwards, the predictions of these equations at the central layer of interphase (the average strength) are compared to the calculations of interphase strength (sigma(i)) by several micromechanical models including the developed Leidner-Woodhams and Pukanszky models to choose the best equation which expresses "sigma(k)". The calculations are carried out for several reported samples. The equation which expresses the "sigma(k)" as a power function of "x(k)" shows the best results compared to others. Also, its predictions significantly depend to an exponent as "Z" which demonstrates the level of interphase properties. According to the chosen equation, the "sigma(m)" and "sigma(p)" play positive roles in "sigma(i)" predictions at low "Z" value, but a high "Z" eliminates the effect of "sigma(m)" on the tensile strength of interphase layers. (C) 2016 Elsevier Inc. All rights reserved.