Nanoparticles have attracted widespread interest in molecular biology and medicine fields for diagnostic application and biological imaging, due to their unique optical properties and facile surface chemistry. Noble metals, especially gold nanoparticles (NPs), have great potential use in biological issue imaging, cancer diagnosis and therapy because of their surface plasmon resonance (SPR) and strong absorption induced luminescence. Au-ligand conjugates can specifically target the receptor on cancer cells, provide specific information about specific molecules, and allow molecular-specific imaging and cancer detection. Gold NPs can strongly absorb light, efficiently convert optical energy into localized heat, produce selective photothermal effect, and induce protein denaturation and cells death. The optical and photothermal properties of gold NPs are summarized, and the research progress of selective targeting of gold NPs in biological imaging, cancer diagnoses and photothermal therapy is reviewed.