Cdc7 protein, a serine-threonine kinase, acts as a regulator in the initiation of DNA replication by phosphorylation, and is also implicated in S phase checkpoint response via the interaction with ATR/Chk1 pathway. A human homologue of Cdc7 (huCdc7) is ubiquitously expressed in human tissues, while is overexpressed and activated in a high level in many tumor cell lines. Recent studies show huCdc7 kinase play an important role in the development and chemical resistance of cancer, and huCdc7 has been accepted as a new biomarker of tumor. More recently, it has been reported that PHA-767491, an efficient inhibitor of huCdc7, suppresses tumor growth without the damage of normal cells. Thus, the insight into huCdc7 kinase and its inhabitors would provide a novel strategy for tumor treatment.