In this study copper nanoparticles were synthesized using the chemical reduction method via solution chemistry. The procedure of preparation of copper nanoparticles in an aqueous solution ata high cupric ion concentration (up to 0.5 M) and without input of extra inert gas, using the hydrazine as the reducing agent and the anionic surfactant, sodium dodecyl sulfate (SDS) as a capping agent was examined. First, we evaluated size distribution, stabil-ity and surface composition of received nanoparticles. Then the antimicrobial activity tests were performed to verify their antibacterial and antifungal activity. The results of these tests performed ona very wide range of the reference and clinical gram-positive strains of methicillin-resistant Staphylococcus and three standard strains of yeast bring the main novelty of the presented work.