In this study, three different ilmenite-limonite (ILC) concretes were modeled in terms of determining the effect of filler type and filler size on the enhancement of radiation shielding properties in the 0.142-1.33 MeV gamma-ray energy range. Accordingly, ILC concrete, micro (50 mu m) and nano (50 nm) WO3, and micro (50 mu m) and nano (50 nm) PbO filler added ILC samples were modeled. MCNPX simulations of micro- and nano-sized particles inside of the ILC sample were performed using lattice (LAT) and universe (U) features of MCNPX (version 2.7.0) code. The greatest increase in mass attenuation coefficient was reported from micro-PbO to nano-PbO filler as 7.88% at 0.142 MeV energy value. The study's findings indicated that decreasing the particle size of the additive material decreases the mean free path and so increases the quantity of gamma radiation interacting per unit distance. Although we validated the consistency of our input against the standard NIST database, several points, such as experimental investigations of nanoparticles in ILC concrete, nanoparticle distributions, and the effect of this distribution on overall shielding enhancement, should be investigated further.