In this work, phosphor and nitrogen co-doped carbon dots (N-P-doped CDs) were developed for bioimaging. The as-synthesized N-P-doped CDs emit a bright blue coloured fluorescence after exposure to a 365 nm UV-lamp illumination. It is also demonstrated that the fluorescence of CDs is resistant to the interference of metal ions, saline solution, and high ionic strength environments. The bright fluorescence nature of the N-P-doped CDs has proven them to be excellent probes for cellular imaging. And this guess is further confirmed by using a laser scanning confocal microscope (LSCM). The viability study was carried out by MTT assay, suggesting the high biocompatibility of N-P-doped CDs. The results demonstrated that N-P-doped CDs may be considered as a safe material for bio-imaging and drug delivery in cancer cells.