A medium-scale lithium-loop with 40 /min and 3bar ratings was constructed to gain basic information on MHD effects on the flow and heat transfer characteristics. The loop has two parallel test sections for pressure drop and heat transfer experiments, which were made of 15.75 mm I.D. and 19.05 mm O.D. 316-SS tubes and placed between magnet poles of 500 mm vertical length. The pressure drop test section was provided with two strain gage type pressure transducers and the heat transfer test section with a 300 mm long 7.6 mm O.D. high flux electric heater pin. The experiment covered the ranges of the magnetic flux density: 0–1.0 T, The Li flow velocity: 0.2 –5.0 m/sec, the heat flux: 0–120 W/cm2 and the Li temperature: 350–400 °C. The experimental results of potential and pressure drop agreed well with the theoretical prediction based on the uniform-velocity thick wall model. The heat transfer coefficient, or Nusselt number, was decreased with increasing magnetic flux density, but not monotonically in a weak magnetic field region of 0.2–0.4 T, where a singular phenomenon , i.e. an elevation of Nusselt number was observed.