Temperature in a test pit of a metal mine was measured during a half month by a distributed temperature sensor. The sensor was optical fiber jacketed by a metal tube. The fiber bound along boring rods was inserted for 145m into the pit. Because of the metal jacket, the fiber sustained less damage by friction against rock around the pit. It stood also corrosion by hot water in the pit for a half month. The measured temperature was biased from the true one because the optical character of the fiber was different from that of the reference fiber constructed in the measuring system. In addition, owing to heat conduction along the fiber, temperature of a hot spot like inflow of hot water into a borehole was affected by temperature in surroundings. In spite of these errors, continuous measurement of temperature distribution by optical fiber helped us to understand the condition in the pit. It showed the change of flow rate in the pit and the difference of geological features of rock surrounding it.
