Measurements of velocity distribution and pressure loss of a turbulent flow of Bingham plastic fluid in rough-walled pipes were made.For the measurements, six rough-walled pipes obtained by gluing geads on the pipe walls with synthetic resin glue and kaolin suspensions of five different densities were used.The relative roughness of pipes and the rheological coefficients of the kaolin suspensions are shown.The experimental results for pressure loss indicate that the friction coefficient value depends on the relative roughness alone and is almost the same as the value of Newtonian fluid flow in the regime and that the coefficient of Bingham plastic fluid in the transition regime is affected by the Reyonlds number, the Hedstrom number and the roughness Hedstrom number.The experimental results for velocity distribution show that the velocity profile of Bingham plastic fluid in the region of transition from hydraulically smooth to rough depends on the roughness Reynolds number, the Hedstrom number and the roughness Hedstrom number, and that the velocity profile in the fully rough region agrees with Eg.(8), which is obtained from the velocity profile of Newtonian fluid flow in the fully rough region by Nikuradse.A mixing length which is suitable for calculating the velocity profile and pressure loss of Newtonian fluid flow in rough-walled pipes is proposed.A guide in assessing the mixing length of Bingham plastic fluid flow in roughwalled pipes is given.