The term underutilized plants refers to categories of plant species whose potential remains largely untapped. In recent times, these plants have gained recognition due to their green synthesis of nanoparticles. Species such as Moringa oleifera, Kaempferia angustifolia, Tephrosia purpurea, Nasturtium officinale, Clerodendrum, and Calotropis have been utilized because they contain significant antimicrobial, anticancer, and antioxidant properties. Secondary metabolites, including terpenes, phenolics, and organic acids, are mainly produced as a defense mechanism, which further helps to fabricate nanoparticles by functioning as reducing and stabilizing agents. Traditional nanoparticle synthesis methods often involve the use of harmful substances. On the other hand, the green synthesis of phyto nanoparticles utilizing plant extracts and phytochemicals introduces a sustainable and eco-friendly substitute. This chapter highlights the ability of underutilized plants to synthesize nanoparticles and emphasizes their phytochemical diversity and therapeutic implications.