A simple formulation of bactericidal cold cream using the biosynthesized silver nanoparticles (AgNPs) from Cassia auriculata flower extract and their antibacterial activity was tested against various clinical pathogens such as Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, and Staphylococcus epidermidis. An ecofriendly method was followed for the biosynthesis of AgNPs using C. auriculata flower extract as a reducing agent at room temperature. The effect of different concentrations of flower extract and the various pH conditions of the reaction medium toward the formation of NPs were studied. Surface plasmon resonance peaks were obtained from 403 nm to 428 nm. Further, the synthesized NPs were characterized by dynamic light scattering particle size analysis, Zeta potential analysis, atomic force microscope, and high-resolution transmission electron microscopic analysis.