Green synthesis of nanoparticles has recently been a preferred method since it offers useful approaches such as non-toxic, biocompatible, environmentally friendly, cost-effective, stable product and trustable alternative processes compared to other methods. Various biological sources such as plant, algae, fungus and bacteria are widely used in biological synthesis of nanoparticles. Algae are more adapted organisms compared to the others for having high growth rate and biomass productivity, high heavy metal accumulation capacity, etc. Nanoparticles can be used in various area such as antimicrobial, antifungal, antioxidant agent, admixture of biosensor and drug transport/release, also diagnosis and treatment systems. Since each organism has different biochemical composition and metabolic pathways, their synthesized nanoparticles are going to show various characteristics and application area. In this study, silver, iron (II) and zinc nanoparticles were produced by using microalga Galdieria sp. The synthesized nanoparticles were characterized by using UV visible spectroscopy, Fourier transform infrared spectroscopy (FTIR) and zeta sizer. Antimicrobial activity against gram negative and gram-positive bacteria was also examined throughout the study. In conclusion, the potential of this biogenic nanoparticle was discussed.