In recent years, biosynthesis and green chemistry are the novel approach for the fabrication of nanoparticles. Cu2O nanospheres decorated graphitic carbonitride (g-C3N4) nanocomposite have been synthesized by hydro thermal method using extracts of Citrus limon leaves which acts as reducing and stabilizing elements for the biosynthesis of nanoparticles. The comparative antimicrobial assay of different mass percentage(1%,5%,10%) of Cu content in the nanocomposites revealed that the CuCN10 has the more effective zone of inhibition due to their average particle size range 2-10 nm. The addition of g-C3N4 as a support for the Cu2O photocatalyst helps in enhancing the charge transfer and improving photocatalytic degradation of contaminants and microorganisms. Moreover, the synthesized composite showed good antibacterial properties against both Gram-negative and Gram-positive bacterial strains.