Protein kinases transfer the γ-phosphate group of ATP to the hydroxyl group of substrate protein. 518 human kinases are classified into serine/threonine kinases and tyrosine kinases, and individually and/or synergistically transduce physiologic stimuli into cell to promote cell proliferation or apoptosis, etc. Kinases are identified as drug targets because dysfunction of kinases leads to severe diseases such as cancers. In this review, I describe structural biology on kinases and drug discovery for the severe diseases such as cancers due to kinase dysfunction.