Metal oxides and their nanocomposites are used in various technological applications. Biofabrication of carbon-based metal oxide nanocomposites preparation using plants, microbes, cell cultures and enzymes are the most attractive technique because of nontoxic nature, and sustainable process. Phytochemicals play important role in size lessening of the particles by performing as structure-directing, capping and reducing agents. In this chapter, we shed light on eco-friendly, money-spinning, and phytosynthesis of carbon based nanomaterials (CNMs) like graphene oxide, reduced graphene oxide, and metal doped-rGO nanocomposites using green reducers. Moreover, electrochemical, photocatalytical and biological applications of CNMs and their nanocomposites with metal oxides are discussed.