In the current study, caffeic acid was an important metabolite in the highly copper-tolerant plant Elsholtzia splendens. Preparation and purification of caffeic acid were performed on the dried biomass of the plants by means of sonication/ethanol extraction, followed by purification using a macroporous resin (D101 type) column and silica gel chromatography. The faint-yellow caffeic acid product was yielded with a purity of 98.46%, and it was chemically identified from spectra of Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance ((1)H NMR)/carbon nuclear magnetic resonance ((13)C NMR), and electrospray ionization mass spectrometry (ESI-MS). Caffeic acid is a possible product from the post-harvest processing of Elsholtzia splendens biomass.