A water soluble 8-aminoquinoline based fluorescent Zn2+ chemosensor (AQZ-2COOH) containing two carboxylic groups has been synthesized. The designed two carboxyl groups not only greatly improved the water solubility of this chemosensor but also increased its affinity for Zn2+. It has been proved that AQZ-2COOH, a pentadentate N, O-chelating ligand was able to coordinate with Zn2+ through three nitrogen atoms and two oxygen atoms, resulting in the formation of a stable Zn2+ complex, and the binding constant between AQZ-2COOH and Zn2+ was determined to be 3.6 × 109 M−1. Furthermore, AQZ-2COOH shows 39-fold fluorescence enhancement upon binding of Zn2+ in aqueous solution. However, this remarkable emission enhancement did not occur when other metal ions were present. Further study revealed that AQZ-2COOH had low biotoxicity, and live cell imaging showed that AQZ-2COOH can be efficiently phagocytized by HeLa cells, a visible green fluorescence from the intracellular area was observed after incubation with AQZ-2COOH and Zn2+ for 3 h, suggesting that AQZ-2COOH can be a promising candidate for detection of mobile Zn2+ in biological systems.