Abstract: In this study, a suspension of nitrogen-doped carbon quantum dots (N-CQDs) was synthesized via a hydrothermal method at 180 °C, utilizing citric acid and urea as carbon and nitrogen precursors, respectively. Dynamic Light Scattering (DLS) analysis revealed that the particle size distribution was predominantly within the range of 2–7 nm. Elemental mapping and Energy-Dispersive X-ray Spectroscopy (EDS) confirmed the uniform distribution of carbon and nitrogen throughout the sample. The ultraviolet-visible (UV-Vis) absorption spectrum exhibited a distinct peak at 300 nm and an absorption edge at 363 nm. Photoluminescence (PL) spectroscopy demonstrated excitation-dependent emission behavior; specifically, the emission peak of N-CQDs shifted from 412 nm to 473 nm as the excitation wavelength increased from 300 nm to 400 nm. Biocompatibility assessment using the MTT assay on the MDA-MB-231 breast cancer cell line indicated high biocompatibility and negligible cytotoxicity of the synthesized N-CQDs. Notably, a cell viability rate of over 80% was maintained at concentrations up to 500 µg/mL after 48 hours of incubation. In conclusion, the synthesized N-CQDs possess favorable optical properties and substantial biological stability, suggesting their potential suitability for biomedical applications, particularly bioimaging.