T h e influence of a transverse magnetic field on the heat transport characteristics of a potassium heat pipe was experimentally studied in the range of field strength 0-0.6T. T h e wick was constituted of a multilayer mesh screen, and the adiabatic section, to which the magnetic field was applied, was made up of a concentric doublewall rectangular tube, with the inner wall completely separating the vapor and liquid flows.T h e magnetic field was applied perpendicularly to the heat pipe, upon which the axial temperature distribution of the heat pipe was observed to be affected, and the heat transport rate to be reduced with increasing field strength.T h e effect of the magnetic field on the heat transport rate is analyzed in terms of the liquid pumping ability of the wick and of the magnetohydrodynamic (MHD) effect on the liquid flow through the wick. T h e MHD effect on the flow through wick is shown to be expressible by a formula similar to that for flow between parallel plates.The heat transport rate measured in magnetic field a r e compared with values calculated assuming that the wick pumping ability was not influenced by the magnetic field but that it w a s the MHD effect on the liquid flow through the wick that affected the heat transport. T h e calculated results well explained the experimental data.