The application of perovskite quantum dots (PQDs) in biomedical fields such as bioimaging and biosensing has been limited owing to their instability in the physiological environment. Herein, PQDs are innovatively encapsulated into nano-micelles composed of a polyethylene glycol-polycaprolactone (PEG-PCL) block copolymer, which allows the preparation of biocompatible PQDs (bio-PQDs) with excellent water resistance. Due to the benefits of extraordinary water resistance and biocompatibility, these bio-PQDs are capable of real-time and long-term quantitatively monitoring the H2S level in living cells as well as in zebrafish.