This study assessed the effect of nano-hydroxyapatite incorporation into resin infiltrant on the mineral content, surface tomography, and resin tag penetration of demineralized enamel. Forty specimens were exposed to a demineralized solution to form subsurface caries lesions. The lesions were treated with negative control, a resin infiltrant (ICON), ICON with 5% nano-hydroxyapatite (NHA, Sigma-Aldrich), or ICON with 10% NHA. Mineral density was assessed using microcomputed tomography scans at various stages of the experiment. Specimens were scanned by scanning electron microscope (SEM) for surface analysis and resin tag penetration. Analysis of variance was used to assess the difference among groups. Specimens treated with ICON and 5% or 10% NHA showed the most favorable mineral density regarding the percent change in mineral content (32.4% and 29.7%, respectively), compared to 8.8% in teeth treated with ICON alone and -1.8% in teeth in the control group. SEM showed that teeth treated with ICON or ICON with 5% or 10% NHA had a smooth surface. The resin penetration in all tested groups showed high-quality resin tags, regardless of the treatment protocol. NHA resin infiltrant (ICON with 5% or 10% NHA) effectively enhanced the artificial enamel caries surfaces in terms of smooth surfaces, mineral density, and resin penetration.