We report in this paper the test results of the Langmuir Probes (LPs) that have been used on several Korean low earth orbit (LEO) satellites since 1999. The probes were designed to measure the electrons in the density range of similar to 10(4) to similar to 10(6)/cm(3) and temperatures less than similar to 10(4) K, which are the typical characteristics of the upper ionosphere. Careful considerations were given to the probe design to reduce many error sources. For example, a 10 Hz fast voltage sweep was applied to the probe to minimize measurement errors caused by probe contaminations. An electron temperature probe was installed in addition to the LP on the KOMPSAT-1, and the electron temperatures measured simultaneously and independently by the two instruments were compared. The results showed good agreement, which confirms the validity of the LP data obtained from these Korean satellites. (C) 2013 Elsevier B. V. All rights reserved.