Nanotechnology is the most fascinating area of research in the field of material science. Biological methods of synthesis of nanoparticles in plants are a quite new approach and continuously gaining popularity in the scientific community due to ecofriendly procedure. When we think about the biological world we normally think of delicate, temperature sensitive, carboneous or organic materials like leaves, stems, roots, cells, tissue, skin etc. inorganic materials are also produced in the biological systems. A variety of mechanically strong or weak, rigid or flexible, porous or nonporous, thick or thin, inorganic or organic material is abundantly produced inside or adjacent to living cells. However, these all are that nature?s secrets that are beyond the human understanding. In this book, silver nanoparticles are biologically synthesiszed within Brassic juncea seedlings and after isolation antibacterial effect of these nanoparticles were examined. This is a quite new approach in the field of Nanobiotechnology.