The MHD pressure drop was measured by providing a lithium circulation loop of 40 lit/min and 0.3MPa head with a square test section of 2a=15.7mm × 2b=15.7mm or a rectangular one of 2a=26.8mm × 2b=ll.lmm inner cross-section made of tw=2.1mm thick 304-SS walls. The experiment covered ranges of B=0.2–1.5T (Ha=200–2100), U=0.2–4.0m/sec (Re=500–38000), and TLi=309–380°C. Theoretical prediction was made on an assumption of a uniform electric current density, neglecting the friction with walls. The MHD pressure gradient -dP/dz is given by -dP/dz = KpσfUB2 where Kp= C/(l+a/3b+C) and C=σwtw/σfa. The theory agreed well with the experimental data for both the square and rectangular test sections. Under the ununiform magnetic field of the exit, the pressure drop data agreed with an approximated prediction of Δ P= ∫KpσfUB2(z)dz.