In recent years, aldehyde-appended fluorescence probes are paid more and more attention by researchers. The fluorescent biological imaging provided many new applications today, which is often used for cell and tissue imaging in biomedical research. Meanwhile, the nucleophilic mechanism is a very simple and convenient procedure for the preparation of aldehyde-sensing probes. This tutorial review focuses on aldehyde-bearing chemosensors based on nucleophilic addition mechanism with biological applications.