In recent time, green synthesis of metal nanoparticles is latest developing technology and received prodigious interest because it is easy, environmentally pristine, non-fouling, antitoxic, and low-cost approach. Green route of biogenic synthesis of metal nanoparticles via microbes such as bacteria, fungi, virus, yeast, algae has the potential to deliver sustainable and envirosafe protocol. Green synthesized metal nanoparticles are the most optimistic and novel agent for various catalytic and biological activities as antibacterial, antiviral, anticancer etc. without any toxic effects. Here we reviewed algae-mediated green synthesis of metal and metal-oxide nanoparticles and their biological activity. Algae are photoautotrophic, eukaryotic, aquatic, unicellular or multicelluler organisms. Algae commonly used for biosynthesis because they grow rapidly, double their biomass on average ten times faster than higher plants and easy to handle experiments with algal species. Different algal strains such as red, green and brown algae used for green synthesis of metal nanoparticles. Algae contain bioactive molecules and secondary metabolites that act as reducing, capping and stabilizing agent for manufacturing in nanoparticles. Biogenically synthesized metal and metal oxide nanoparticles characterized by different techniques such as UV-visible spectroscopy, SEM (scanning electron microscopy), HR-TEM (high-resolution transmission electron microscopy), XRD (x-ray diffraction), TGA (thermo gravimetric analysis), DLS (dynamic light scattering) zeta potential and exhibited biological activity. In future research algal production of metal nanoparticles can be explore by the use different microalgae and their applications in different areas such as biological activity, catalytic activity in synthesis of organic compounds, medical diagnose and synthesis of nanocomposite, lipid nanoparticles, antibiofilm.