ABSTRACT Matrix‐assisted laser desorption/ionization mass spectrometry imaging (MALDI‐MSI) has rapidly advanced in biomedical research, enabling label‐free, untargeted spatial detection of metabolites, lipids, proteins, and glycans in tissue sections. However, challenges such as low ionization efficiency and chemical instability limit the detection of certain molecules. To address these issues, on‐tissue chemical derivatization (OTCD) has been widely applied as an effective strategy to enhance imaging capabilities. This review systematically summarizes the development of derivatization reagents targeting different reactive functional groups and their applications in MALDI‐MSI, including strategies for the derivatization of amines, carbonyls, carboxyls, double bonds, hydroxyls, thiols, and platinum‐based drugs. Particular attention is given to how these derivatization reagents enhance the detection range and biological relevance by increasing molecular weight, improving ionization efficiency, and reducing background noise interference. Additionally, we explore the application of OTCD in various biological samples and discuss challenges related to experimental workflows, derivatization efficiency, and tissue integrity. This review provides important theoretical support for the advancement of MSI technology and highlights its broad potential applications in biomedical research.