Cu20 nanoparticles have become of growing interest for their applications in catalysis and electronics; however, few environmentally friendly and straightforward synthesis processes exist to produce these nanomaterials. 1-4 With the potential need for efficient nanoparticle syntheses in industry, the world of plant-based reducing agents has become of interest for their great availability and low environmental impact.5-8 Herein, I describe a onepot synthesis via the reducing agents in lemongrass to produce 1-10 nm spherical Cu20 nanoparticles of a fluorescent nature. These particles have been characterized using UV-visible spectroscopy (UV-vis), fluorescence spectroscopy, high resolution transmission electron microscopy (HR-TEM), powder X-ray diffraction (XRD), and atomic absorption spectroscopy (AA). They display a small absorbance in the visible range and have a sizedependent fluorescence emission band near 453 nm. The relative quantum yield of these particles was found to be 0.0061±0.0019, an order of magnitude larger than some other Cu20 nanoparticles. 3 HR-TEM imaging reveals a lattice spacing of 2.4 Å, indicating the Cu20 oxidation state. In addition, particle size control has been demonstrated by varying reactant ratios within the synthesis mixture. This room temperature, one-pot synthesis shows promising results for producing Cu20 nanoparticles in a low cost, environmentally friendly process.