DGKα, also named diacylglycerol kinase alpha, plays an important role in signal transduction, phosphorylating the membrane lipid diacylglycerol (DAG), to phosphatidic acid (PA). Increasing evidence indicates that DGKα-mediated T-cell dysfunction plays a significant role in the development of resistance of the PD-1 blockade. In this article, we report the discovery of compound 16 as a novel, potent, orally available DGKα inhibitor with excellent kinase selectivity, a favorable ADME profile, and robust in vivo antitumor activity in combination with anti-PD-1 therapy.