The current investigation employed an aqueous waste peel extract of Citrus sinensis (Family: Rutaceae) to fabricate monometallic (silver (Ag), (gold (Au), and bimetallic silver –gold alloy nanoparticles (Ag: Au alloy NPs). The results proved that pH 8 and 30 ^oC are optimal for producing (Ag, Au, and Ag: Au alloy NPs) utilizing peel extract of Citrus sinensis as reducing as well as stabilizing agents. The visual investigation of the bio-synthesized (AgNPs, AuNPs, and Ag: Au alloy NPs) indicated that the color shift from colorless to yellow-brown, violet, and purple, respectively. UV-visible spectroscopy has been employed to establish the synthesis of AgNPs, AuNPs, and Ag₁:Au₁ alloy NPs, each with unique characteristics absorbance peaks at 424, 545, and 498 nm, respectively. Ag and Ag: Au alloy NPs exhibited different antibacterial activities against Pseudomonas aeruginosa when biosynthesized at different temperatures. The pronounced antibacterial activities were achieved at 30^oC, whereas at high temperatures (60 ^oC), they showed a minor effect. Bio-fabricated mono and bimetallic nanoparticles showed that Gram-negative bacteria tend to be more vulnerable because of their cell wall composition. We will try to find out more medical applications of Ag-Au alloy nanoparticles.