Abstract: Chemical exchange saturation transfer (CEST) magnetic resonance imaging (MRI) is an advanced imaging method that probes the chemical exchange between bulk water protons and exchangeable solute protons. This chemical exchange decreases the MR signal of water and reveals the distribution and concentration of certain endogenous biomolecules or extrogenous contrast agents in organisms with high sensitivity and spatial resolution. The CEST signal depends not only on the concentration of the CEST contrast agent and external magnetic field but also on the surrounding environments of the contrast agent, such as pH and temperature, thus enabling CEST MRI to monitor pH, temperature, metabolic level, and enzyme activity in vivo. In this review, we discuss the principle of CEST MRI and mainly summarize the recent progress of diamagnetic CEST (diaCEST) contrast agents on tumor imaging, diagnosis, and therapy effect evaluation.