A theoretical method has been discussed to study the size dependency of thermal expansion of nanomaterials at higher temperature by considering the surface effect. A thermodynamical analysis of the equation of state (EoS) is studied from the knowledge of thermal expansion of nano-materials based on theoretical thermodynamical relations. It is observed that thermal expansion coefficient increases with decrease in grain size whereas, 𝑉/𝑉₀ increases with increase in temperature for nanomaterials of different grain sizes. We have studied the size and temperature dependence of thermal expansion of Cu, Ag, Ni, Sn, Se and Zn nanomaterials in different shapes (spherical, nanowire and nanofilm). The available experimental data confirm these theoretical predictions that demonstrate the validity of our work.