The present thesis deals with isolation of marine microorganism Streptomyces hygroscopicus for synthesis of metal nanoparticles and their applications. The thesis divided by five chapters. Chapter 1 explains the overview of biological synthesis of nanoparticle and their applications. Chapter 2 demonstrates the screening and characterization of S.hygroscopicus-morphological and molecular characteristics including 16S rRNA sequencing. Furthermore the present study reports physiological characterization of crude extract isolated from S.hygroscopicus by UV, FTIR, NMR and MASS analysis. Chapter 3 explains biosynthesis of silver nanoparticles (Ag-NPs). Biological reduction of aqueous silver ions by extracellular components of S.hygroscopicus has facilitated the development of industrially viable greener methods for the synthesis of technologically important Ag-NPs. The synthesized nanostructures are characterized by UV/Vis, XRD and energy dispersive X-ray analysis. Particle morphology is characterized by TEM, FE-SEM and BioAFM. Furthermore, the biosynthesized Ag-NPs significantly inhibited the growth of medically important pathogenic micro organisms. Thus; bioconversion of silver nanoparticles by S. hygroscopicus could be employed as a potential nanomedicine to eliminate pathogenic microorganisms. Chapter 4 explains cytotoxicity activity of Ag-NPs against A549 and IMR90 cells. The present study investigates the biosynthesized Ag-NPs induced death response in human carcinoma lung cell line A549 and fibroblast cells IMR90 by XTT assay. Gradual increase in Ag-NPs concentration induces the death response. Notably, at higher Ag-NPs concentration there was an asymmetric accumulation in the nucleus of the A549 cells. The toxicity was evaluated using changes in cell morphology, cell viability, and oxidative stress by FE-SEM and confocal lase scanning microscopy. Chapters 5 demonstrate the biosynthesis of single-pot room-temperature reduction of aqueous chloroaurate (AuCl₄-) ions by S.hygroscopicus cells. The present Study reports polygonal Au-NPs are generated via the manipulation of key growth parameters, including solution pH, ion concentrationand reaction time. The synthesized nanostructures are characterized by UV/Vis and energy dispersive X-ray analysis studies. Particle morphology is characterized by HR-TEM, FE-SEM and Bio-AFM. Additionally, furthermore we have demonstrated the electrochemical and antibacterial and cytotoxic properties of Au-NPs via cyclic voltammetry analysis and a minimal inhibitory concentration and MTT assay. The toxicity of Au-NPs has been investigated at the cellular level using HeLa and 293T cells. Present findings exhibit that Au-NPs enter cells in a size- and shape-dependent manner. Owing to the drawbacks of chemical synthesis, a biological synthesis method has been developed to generate biocompatible, inexpensive and eco-friendly size-controlled nanoparticles.