The reliable information on the hydraulic characteristics of rock mass is one of the key site factors for design and construction of deep subsurface structures such as geological radioactive nuclear waste disposal repository, underground energy storage facility, underground research laboratory, etc. In order to avoid relying on foreign field test technology in future projects, we have independently designed and made integrated type main frame, 120 bar waterproof downhole sonde, and 1,200 m wireline cable winch through a series of R&D activities. They are core apparatuses of the Deep borehole Hydraulic Test System (DHTS). Integration of individual test equipment into a single main frame allows safe and efficient work in the harsh field condition. The DHTS was developed aiming primarily for constant pressure (head) injection test and pulse test in deep impermeable rock mass. The maximum testing depth of the DHTS is about 1,050 m from the surface. Using this system, it is possible to make precise stepwise control of downhole net injection pressure in less than 2.0 kgf/cm2 with dual hydraulic volume controller and also to inject and measure the very low flow rate below 0.01 l/min with micro flow rate injection/control module. Over the past two years, we have successfully completed more than 50 in situ hydraulic tests at 5 deep boreholes located in the Mesozoic granite and sedimentary rock regions in Korea. Among them, the deepest testing depth was more than 920 m. In this paper, the major characteristics of the DHTS are introduced and also some results obtained from the high precision field tests in the deep and low permeable rock mass environment are briefly discussed.