In the field of nanotechnology one of the important processes was to develop an eco-friendly method of preparing metallic nanoparticles by using natural sources which are available in the globally. To achieve the eco-friendly process of synthesizing nanoparticles several natural sources such as bacteria, fungi, actinomycetes, plant materials, and marine microbials were used. In this chapter we discuss the synthesis of transition metal nanoparticles, such as gold, silver, platinum, and cadmium using various marine microorganisms, including bacteria, cyanobacteria, yeast, fungi, algae, and also some marine animals like finfish and sponges. Hence, this chapter brings out the application of marine sources in the preparation of various nanoparticles. © 2016 Elsevier Inc. All rights reserved. All rights reserved.