Fluorescent carbon-based nanomaterials, including carbon dots (C-Dots) and the emerging graphene quantum dots (GQDs) are attracting increasing interest in the field of biosensing and bioimaging for their high aqueous solubility, stable photoluminescence (PL), low cytotoxicity, good biocompatibility as well as superior resistance to photobleaching. Compared with C-Dots, the quasi zero-dimensional (0D) GQDs with a few atomic layers can exhibit strong PL without passivation. With these extraordinary properties, GQDs are suitable alternatives as both a versatile platform for biosensing and a promising class of bioimaging probes. In this review, we introduce the synthesis, structure, PL properties and currently available applications of GQDs in biosensing and bioimaging field. We hope this review will provide critical insights to inspire more exciting researches on GQDs for biological applications to better realize the potential of the intriguing GQDs in the near future.