Chemical corrosion and bio-corrosion in water pipelines are the most common problem in the industry worldwide which cause damage to expensive equipment and increase the maintenance costs. In the current study, the nanocomposite composed of ZnO and CuO nanoparticles was successfully synthesized using brown algae (Sargassum muticum) extract and then dispersed in polyethylene oxide polymer. The synthesized nanoparticles were exposed to gamma radiation to reduce their particle size. The synthesized nanocomposites were characterized using UV-vis spectroscopy, Dynamic light scattering (DLS), X-ray diffraction (XRD), Transmission electron microscopy (TEM), and FTIR analysis, then, the anti-biofilm and anti-adherence efficacy of nanocomposite were evaluated. The results revealed that gamma radiation reduced the particle size of ZnO and CuO nanoparticles to l5 and 20 nm, respectively. Also, the results showed a significant reduction (P < 0.001) in biofilm formation and adherence of Proteus mirabilis (P. mirabilis), Pseudomonas aeruginosa (P. aeruginosa), and Staphylococcus aureus (S. aureus) to carbon mild steel coupon C1010. In addition, from all the tested strains, P. mirabilis caused the highest bio-corrosion rate 1.5 mpy on mild steel coupon and nanocomposite prevented its adhesion as confirmed by Scanning electron microscope (SEM). Furthermore, the nanocomposite at 150 ppm showed the highest anti-corrosion activity 92.3% in 1 M HCl and exhibited mix-type inhibitor (cathodic and anodic). Finally, the results concluded that the green synthesized nanocomposite had multi-function to be used as anti-biofilm, bio-corrosion inhibitor, and anti-corrosion.