Sorghum stem (Sorghum bicolor L.) is a plant that has not been maximally utilized. But sorghum stems contain high cellulose. The hydroxyl (OH-) and carboxyl (-COOH) groups on cellulose can bind heavy metals; therefore, sorghum stems have the opportunity to be used as an adsorbent to absorb heavy metals, especially Cu(II) metal, which can pollute the environment. Therefore, this research was conducted to determine the optimum pH, contact time, and the adsorption capacity of Cu(II) using HNO3 modified sorghum stem adsorbent. The stages of the research included the preparation of sorghum stem adsorbent, modification of adsorbent with HNO3, determination of optimum pH, optimum contact time and adsorption capacity of Cu(II) metal. Furthermore, the functional groups of the adsorbent before and after modification were determined by FTIR. SEM-EDS to assess the morphological structure and chemical components contained in the adsorbent. After the research, the optimum pH of Cu(II) metal adsorption was pH 6, and the adsorption power was 99.88%. The optimum contact time is 10 minutes. The percent removal of Cu(II) metal with concentrations of 10, 30, 50, and 100 ppm were 79.96; 79.90; 56.40 and 54,04 %, respectively. Adsorption of Cu(II) metal using HNO3 modified sorghum stem adsorbent followed the Freundlich isotherm pattern compared to Langmuir with R2 = 0.9039. It is concluded that activated sorghum stem can be used as Cu(II) metal adsorbent.