Copper nanoparticles are one type of metal nanoparticles that have not been widely studied. Copper nanoparticles have some uniqueness that affects their optical, catalysis and conductive properties. In addition, nanoparticles can also be applied in the field of microbiology because of their antibacterial activity. This study aims to determine the optimum conditions for the synthesis of copper nanoparticles, using melinjo leaves extract as bioreductor. This research used copper (II) sulfate as a precursor. Melinjo leaves are extracted with water at 60°C. Beta cyclodextrin was used as a stabilizer. The results showed that the optimum conditions for the synthesis of copper nanoparticles were using a ratio of extracts: CuSO4 solution: beta cyclodextrin 10 mg/mL = 1: 2: 2 (v/v/v). Nanoparticles were synthesized by reflux at 90°C for 4 hours. The optimization results show that the sonication process for 4 hours after synthesis affects the stability of the formed nanoparticles. Copper nanoparticles have an average particle diameter of 682.8 nm and polydispersity index of 0.497. Copper nanoparticle synthesis conditions can be used routinely in the laboratory for further investigation as a topical antibacterial candidate.