Magnesium nanoparticles (MgNPs) and silver nanoparticles (AgNPs) were synthesized by green synthesis method using Hydrangea paniculata flower extract. The occurrence of various organic molecules like terpenoids, steroids, saponins, alkaloids, quinone, glycosides and flavonoids in the flower was revealed by phytochemical and gas chromatography-mass spectrometry analyses. The formation of brown and black colloids, confirmed the presence of MgNPs and AgNPs, which was further supported by ultraviolet-visible absorbance at 360 and 450 nm by MgNPs and AgNPs. The X-ray diffraction analysis confirmed the cubic phase of MgNPs and AgNPs. FTIR analysis showed the presence of functional groups on the biosynthesized nanoparticles surface. The SEM and TEM analyses demonstrated the formation of spherical and ellipsoidal MgNPs and AgNPs. MgNPs was about 56-107 nm in size, whereas AgNPs was approximately 36-75 nm. In addition, both MgNPs and AgNPs showed excellent antioxidant potential and antibacterial activity against Escherichia coli and Staphylococcus aureus. The current green synthesis method using H. paniculata flower extract is a simple and an eco-friendly approach to synthesize MgNPs and AgNPs for making beneficial health care products. (C) 2016 Elsevier B.V. All rights reserved.