Kinase-catalyzed protein phosphorylation is an important biochemical process involved in cellular functions. We recently discovered that kinases promiscuously accept γ-modified ATP analogues as cosubstrates and used several ATP analogues as tools for studying protein phosphorylation. Herein, we explore the structural requirements of γ-modified ATP analogues for kinase compatibility. To understand the influence of linker length and composition, a series of ATP analogues was synthesized, and the efficiency of kinase-catalyzed labeling was determined by quantitative mass spectrometry. This study on factors influencing kinase cosubstrate promiscuity will enable design of ATP analogues for a variety of kinase-catalyzed labeling reactions.