Background and aims <p>Herpes Simplex Virus Type 1 (HSV-1) has been found to present many therapeutic challenges due to the problem of drug resistance and the low efficacy of antiviral compounds. Recently, the photocatalytic property and biocompatibility of graphitic carbon nitride (g-C₃N₄) nanosheets have been found to be promising for antiviral therapy. The antiviral efficacy and biocompatibility of the g-C₃N₄ nanosheets are assessed in this study.</p> Methods <p>g-C₃N₄ nanosheets were prepared and characterized by X-ray diffraction (XRD), Fourier Transform InfraRed Spectroscopy (FTIR), Field Emission Scanning Electron Microscopy (FESEM), and zeta potential measurements to confirm the properties. Antiviral efficacy was determined by the ability of g-C₃N₄ to block the infection of Vero cells by HSV-1 using two different methods: the virucidal assay and the post-treatment assay. The Real-Time PCR measured viral replication. The cytotoxic effect of the g-C₃N₄ nanosheets was evaluated using a neutral red uptake assay.</p> Results <p>g-C₃N₄ nanosheets exhibited a pure graphitic structure, high colloidal stability, and a porous, flake-like morphology. They achieved dose-dependent HSV-1 inhibition rates of 94.9–99.2% (virucidal) and 92.3–96.0% (post-treatment) at 600–800&#xa0;µg/mL (<i>P</i> &lt; 0.001). No cytotoxic effects were seen in the g-C₃N₄ nanosheets; however, increased cell viability by nearly 40% was seen when tested at a concentration of 800&#xa0;µg/mL.</p> Conclusion <p>g-C₃N₄ nanosheets possess excellent biocompatibility and the ability to inhibit HSV-1 greatly, and are promising alternatives to conventional treatment regimens. There is a need to study further the mechanism of the antiviral properties of g-C₃N₄ nanosheets and the efficacy of g-C₃N₄ nanosheets in vivo.</p>