<p>This study aims to assess the performance of epoxy-based nano-modified composites as surface treatment for mortar samples under H₂SO₄ acid attack. Besides neat epoxy and epoxy/solvent mixture, nano-clay and nano-SiO₂ at three different dosages (i.e., 0.5%, 1.5%, and 3%) were dispersed in the epoxy/solvent mixture and applied to the mortar surface. The changes in the mass and crushing load of the coated samples after immersion in 5% H₂SO₄ solution for 14, 28, and 42 days were compared with those of uncoated mortars. The results of this study were found through SEM observation, EDS element mapping, and rheological measurements. Visual observation of the mortar samples showed that the uncoated samples suffered the most deterioration during immersion in 5% H₂SO₄ solution, indicating a beneficial effect of the mortar surface treatments. Furthermore, the epoxy/solvent mixture, due to its lower viscosity, can fill surface holes and defects and compared to neat epoxy, improve the acid resistance of the mortars. Additionally, mortars coated with 1.5% nano-clay, or nano-SiO₂ modified epoxy/solvent mixtures had the highest resistance against H₂SO₄ acid attack. As confirmed by SEM/EDS observation, using nanoparticles at 3%, because of the tendency to agglomerate in epoxy/solvent mixture is not an appropriate mixing dosage.</p>