Here, we developed an in situ labeling approach to identify exosome-loaded proteins, which bypasses the traditional exosome isolation steps. In this method, an engineered ascorbate peroxidase targeting to endosomes-destined exosomes was used to label proteins loaded inside exosomes released from kidney proximal tubule-derived cells. Mass spectrometry analysis of the kidney proximal tubule-derived cells identified oxidative stress-induced exosome proteome alteration.