Gold nanoparticles (AuNPs) can be readily synthesized and modified with chemical and biological molecules, making them attractive inorganic biomaterials for drug delivery and molecular diagnostics. The surface of AuNPs supports the efficient attachment of various biomacromolecules via chemisorption, chemical conjugation and electrostatic interaction. Based on advantages of facile surface modification and unique optical properties, AuNPs have been extensively used as drug carriers for the intracellular delivery of therapeutics as well as molecular nanoprobes for detection and monitoring of the target molecules of interest. In this review, we highlight advanced approaches in the biomedical applications of AuNPs such as gene and drug therapy, molecular diagnostics and imaging.