The Ulumbu Geothermal Power Plant (PLTP) is located at Mount Poco Leok, East Nusa Tenggara, Indonesia, with a capacity of 10 MW. Ulumbu PLTP has three production wells, analysis of potential scaling problems is needed to determine the scaling potential of UL-02 as a production well and planned UL-03 as planned for production well. Results of fluid samples A-03 and scale test results from A-02 samples show differences elemental and mineral dominant. The element that dominates from sample scale of UL-02 is Silicon (Si), that’s indicate potential scaling silica problem SiO2. In contrast to the test results of the UL-03 fluid sample, it shows dominant bicarbonate and indicate potential carbonate scaling problem at wellbore. The differences scaling products due to differences rock types at production zones of UL-02 and UL-03. The production well from UL-03 penetrates to Mudstone-Limestone & Sandstone rocks. The UL-02 well penetrates only volcanic rock, so the scaling product is dominated by silica scaling. The products from UL-03 and UL-02 scaling tend to be different, and detail result show in this paper. Calculations using Silica Saturation Index (SSI) and Larson Index (LI) completed the potential for scaling will occur when the well is produced.