Eco-friendl nanoparticles research is one of the fascinating branches of nanotechnology science. Among various metal nanoparticles, gold nanoparticles (AuNPs) have attracted huge scientific and technology attention due to their nontoxicity, stability, nano-size structure, etc. AuNPs are inert in many biological environments and carry several physical properties which play an important role in biomedical applications. To date, AuNPs have been successfully employed in tumor radiotherapy, drug carriers, biomedical imaging, biosensors, antimicrobial agent, photocatalyst, antidiabetics, etc. Distinct from other reviews, in this chapter we present the green chemical approach for the preparation and remarkable biological activity of AuNPs. © 2018 Scrivener Publishing LLC.