Determination of local boundary shear stress is an important topic in hydraulic engineering. When attempting to determine this from a very thin boundary region, it is a difficult one because it requires special skills and instruments to treat the measured data. With the advent of new equipment, like the acoustic Doppler velocity profilers (ADVP), all the velocity profiles in the primary flow region can be simultaneously measured, and it is necessary to develop a new method to estimate the boundary shear stress using the primary flow data. This paper presents such a method called the momentum balance method (MBM). A theoretical relationship between the boundary shear stress and parameters of the primary flow region has been established. The results obtained from MBM agree reasonably well with other methods, indicating that the new method is workable in closed duct flows, and possibly its applicability can be extended to a wide range of boundary conditions.