Abstract: Cancer, also known as malignant tumor, is the second largest disease after heart disease, which is characterized by genomic instability and mutagenicity. Ataxia telangiectasia and RAD3-related kinase (ATR) are members of phosphatidylinositol 3-kinase (PIKK) family, belonging to serine/threonine kinase, one of the key kinases in DNA damage response (DDR) and DNA repair pathway. This paper reviews the latest progress in the ATR inhibitor field including mechanism of action (MOA), therapeutic applications, and the combination therapy from the perspective of medicinal chemistry. It also discusses the possible challenges and future directions of developing ATR inhibitor antitumor drugs, which could provide the scientists in this field the convenience for access the information and application guidance for clinical studies.