A new dendrimer based on citric acid and sebacoyl chloride was synthesized by Steglich esterification. The obtained dendrimer was used as a matrix for the dispersion of copper nanoparticles using classical and ultrasound methods. All materials were characterized by FTIR, 1H NMR, thermogravimetric analysis, X‐ray photoelectron spectrometry, scanning electron microscopy, and energ‐y‐dispersive ‐X‐ray spectroscopy. The obtained nanocomposites were tested against two Gram‐positive pathogenic bacteria (Bacillus cereus and Staphylococcus aureus), two Gram negative (Escherichia coli and Pseudomonas aeruginosa), the organic dye methylene blue, and in the 1,1‐diphenyl‐2‐picrylhydrazile radical scavenging assay. A comparative study between both methods in structural, morphological, and thermal properties as well as in the antimicrobial, antioxidant, and catalytic reduction activities was provided. All nanocomposites showed an excellent activity for all applications. The comparison between both synthesis methods shows the superiority of the sonication methods, especially via the catalytic reduction and the antioxidant activities, the classic method allows better thermal stability and a higher metal content with some cationic oxidation state in the obtained nanocomposites, but ultrasound allows a better dispersion with a fully reduced metal.