Graphitic carbon nitride, g-C3N4, is a fascinating candidate for biomedical applications. Of course, bulk g-C3N4 is not appropriate for this purpose due to its large size distribution and low dispersion in water. Herein, for the first time, the electrophoretic size fractionation of g-C3N4 without introducing some functional groups into its structure was performed within a very short time. This simple separation technique resulted in several factions. The smallest collected fraction was nanosheets and showed the enhanced photoluminescence properties such as high PL intensity and bright luminescence. The nanosheets demonstrated significantly higher toxicity (IC50 of 27.0±4.2μg/ml- after 48h) against human bone carcinoma cell line, Saos-2, in the absence of external light source compared to the bulk g-C3N4 (IC50 of 104.0±8.5μg/ml- after 48h) without any cytotoxic effect on normal cells, human foreskin fibroblast.