Exosomes have been deemed as hopeful liquid biopsy biomarkers for malignant tumor identification. However, proposing detection methods with high sensitivity still meets challenges. Herein, we have fabricated an elec-trochemical biosensor in this work via constructing nucleic acid functionalized covalent organic framework (COF) capsules for sensitive detection of exosomes. Firstly, nucleic acid functionalized COF capsules are prepared by modifying azide-labeled DNA onto alkynyl-containing COF capsules. Then, the capsules are used to fabricate an electrochemical biosensor for exosomes quantification. In this design of the sensor, the modification of DNA strands on COFs can greatly improve the binding efficiency, while the loading of plentiful horseradish peroxidase (HRP) facilitates signal amplification. So, the fabricated biosensor has effectively enhanced the sensitivity and lowered the detection limit to 87 particles/mu L. Further studies show that the biosensor can be used for the identification of exosomes from non-small cell lung cancer. Moreover, by simply replacing the DNA sequences, the proposed strategy can generally be used to fabricate different DNA-COF capsules with diverse functions for broader biomedical applications.