The cosmic-ray elemental spectrum is important to understand the generation and acceleration mechanism of high-energy cosmic rays. The Cosmic Rays Energetics And Mass (CREAM) experiment on the International Space Station (ISS) plans to measure nuclear and electron energy spectra precisely. The separation of electrons from protons is crucial because the proton flux is about 1000 times higher than that of electrons in the energy range 300 GeV ∼ 800 GeV. The Top Counting Detector (TCD) and Bottom Counting Detector (BCD) are designed to optimize e/p separation. The TCD and BCD each consists of a plastic scintillator and an average of 400 photo-diodes, respectively. The TCD and BCD are located immediately above and below the calorimeter, respectively. This detector configuration provides e/p separation by using the different shapes of electromagnetic and hadronic showers. We have characterized the performance of the TCD/BCD in several different ways. The signal to noise ratio of the detector cell components was measured by using a90Sr radioactive source and a high-energy beam at CERN. The temperature dependence of the detector cell component, from -40◦C to 70◦C, and the robustness of the TCD/BCD module were confirmed using thermal and vacuum chambers. We present the TCD/BCD design considerations and a summary of the measured performance of the TCD/BCD modules.