In this Chapter well, defined silver nanoparticles were synthesized by using Flower Extracts of Caesalpinia pulchirrima. After exposing the silver ions to the Flower Extracts of Caesalpinia pulchirrima, the rapid reduction of silver ions led to the formation of stable AgNPs in solution due to the reducing and stabilizing properties of Flower Extracts of Caesalpinia pulchirrima juice. The synthesized NPs were analyzed by ultraviolet-visible spectroscopy. The as-synthesized AgNPs were phase pure and well crystalline with a face-centered cubic structure. The antimicrobial activity of the synthesized AgNPs was investigated against Escherichia coli and Pseudomonas aeruginosa by agar well diffusion method. This newly developed method is eco-friendly and could prove a better substitute for the current physical and chemical methods for the synthesis of AgNPs.