Gold nanorods (GNRs), which strongly absorb near-infrared (NIR) light, have shown great potential in fields of biomedical application. These include photothermal therapy, molecular imaging, biosensing, and gene delivery, especially for the treatment of diseased tissues such as cancer. These biomedical applications of GNRs arise from their various useful properties; photothermal (nanoheater) properties, efficient large scale synthesis, easy functionalization, and colloidal stability. In addition, GNRs do not decompose and have an enhanced scattering signal and tunable longitudinal plasmon absorption which allow them to be used as a stable contrast agent. Therefore, GNRs are also promising theranostic agents, combining both tumor diagnosis and treatment. In this review, we discuss the recent progress of in vitro and in vivo explorations of the diagnostic and therapeutic applications of GNRs as a component of cancer therapy.