With the development of nanotechnology, many novel nanomaterials with unique properties such as magnetic, electronics, and photonics are increasingly being exploited. Gold nanorods, which are rod-shaped nanomaterials, show powerful potential in biological/biomedical fields, especially photothermal therapy, biosensing, imaging, and gene delivery for the treatment of cancer. Many scientific groups have shown strong interests in gold nanorods and have attempted to push them towards possible clinical applications. However, owing to the quantum-size effects of nanomaterials, people have also raised some concerns about the potential toxicity hazards. Therefore, it is becoming urgent to study and exploit the biological effects of gold nanorods for benefit in the near future.