Abstract: Carbon dots (CDs), as a novel class of carbon-based nanomaterials, have attracted tremendous attention in biomedicine owing to their excellent optical properties, low toxicity, good water solubility and easy surface modification. In this review, we introduce various methods for their synthesis based on technology and recent research progress on red-emission and near-infrared emission CDs, and address the use of CDs in the diagnosis and therapy treatment of tumors. The review also summarizes the limiting factors that affect the development of CDs and possible new advances.