Cancer is one of the major health problems. Although traditional therapies have been effective in cancer treatment, they often have adverse side effects due to their nonspecific action on both normal and tumor cells. Therefore, targeted treatment strategies using small molecule inhibitors are being extensively studied. These compounds are usually ≤500Da size and are often administered orally. In principle, small molecule compounds can be developed to target any portion of a molecule, regardless of the target’s cellular location. In this blog entry, we provide a summary of the small molecule inhibitors (SMIs) used in the cancer therapy.