The fully developed steady laminar flows of incompressible Bingham plastic fluid through a pipe of circular cross section coiled in a circle were simulated numerically. The flow patterns were characterized by the Dean number De, Hedstrom number He which means the ratio of the yield stress of plastic fluid py to the plastical viscosity ηs, and the curvature ratio δ. Calculations were carried out in the range 50≤De≤200, 0≤He≤1000, for the curvature ratio δ=0.05. It was clarified that the values of the friction facter λc were greater than that of Newtonians in case of low Dean number and were in good agreement with that of the available experimental data. It was also found that in case of a plastic fluids, the magnitudes of the velocity gradients of secondary flows near the wall were greater than that in case of a Newtonian fluid, in the axial velocity distributions a typical plug flow area appeared near the outer side of the vent in case of plastic fluid and that apparent viscosity had a sharp peak at the axial velocity maximum.