Fluorescent bio-imaging has become a major topic of the modern biomedical research field. Fluorescent metal nanoclusters have been proposed as sensitive optical imaging probes aiming for early cancer diagnosis. We have developed a new strategy for the facile synthesis of Au-BSA nanoclusters (NCs) which have stable and bright fluorescence and could be used as a fluorescent probe for bioimaging rapidly and effectively. In this contribution, we have synthesized Au-BSA NCs at 80 °C for 10 minutes with the pH value of 11.5. At the concentration range of 0.1–10 mg mL⁻¹, Au-BSA NCs have no obvious cell cytotoxicity effect on MCF-7, HeLa, L02, U87, and A549 cells. Then the as-prepared Au-BSA NCs were characterized by using TEM and XPS and applied for rapid tumor imaging. The biocompatible BSA stabilized fluorescent gold nanoclusters (NCs) synthesized through one-step hydrothermal reaction possess strong and bright fluorescence that can be readily utilized as a highly sensitive fluorescence probe for tumor-targeted bio-imaging in vitro and in vivo.