Cancer is one of the leading causes of death worldwide and poses a great threat to human health. In the past few years, diverse molecular devices have been constructed by using DNA molecules as the basic units, such as DNA framework-based molecular devices, DNA walking devices, and DNA biocomputing devices. These molecular devices are endowed to accomplish specific behaviors in chemical and material systems, ranging from simple mechanical motions to complex logic operations. Benefiting from inherent biocompatibility, excellent programmability, and functional variability, DNA-based molecular devices hold great promise in cancer diagnosis and have made impressive progress in this field. Herein, we aim to provide an overview of recent advances in DNA-based molecular devices for cancer diagnosis by highlighting several representative works. Specific attention is focused on the analysis of cancer biomarkers at both in vitro and in vivo scenes. New frontiers and opportunities in this field are also discussed from a clinical perspective.