In this paper, frictional constraints of biped robot’s sole is investigated and verified. Conventionally, the studies of frictional constraint in walking have only considered in translational slip. But there are not only translational slip but also twist in actual biped walking. In this study, a method to calculate the frictional force and torque is suggested as the quantitative expression of frictional constraint based on a biped robot model. The frictional constraints were verified the proposed calculation approach of the frictional force and torque by generating pseudo slips.