A theoretical model for the specific heat of nanofluids containing oxide-based nanoparticles of different sizes and at different temperatures has been presented. The model proposed by Xuan and Roetzel has been modified by incorporating the effect of semi-solid interfacial layer, which is formed due to adsorption of base fluid molecules on the surface of nanoparticles. The contribution of this layer has been taken into account by assuming that the heat capacity, as well as the density of interfacial layer, lies between the corresponding values for the nanoparticle and the fluid and as such these have been estimated by taking the arithmetic and the geometric means of the relevant quantities. It is observed that the specific heat capacity of the nanofluid decreases with increase in particle volume fraction and that the presence of interfacial layer enhances the value even though its thickness has been taken to be only 1-2 nm as estimated by Xue et al. using molecular dynamics simulation. The effects of interfacial layer thickness, nanoparticle size, volume fraction, and specific heat ratio of particle to fluid have been discussed. The obtained results are in good agreement with some recent available experimental data.