Our primary objective is to correlate damping predictions from a quasi-steady Bingham plastic damper analysis with experimentally measured steady state damping levels for a magnetorheological (MR) fluid damper. We seek to characterize damper properties of yield force and post-yield damping, and relate the damper parameters to effective MR fluid properties of dynamic yield stress and plastic viscosity. This characterization is done as a function of applied field and frequency. The damper was mounted in a mechanical scotch-yoke type damper dynamometer. The damper shaft was displaced sinusoidally with 1 inch of stroke and the resulting steady state force was measured as a function of applied current and frequency. The resulting force vs. displacement and force vs. velocity data is used to characterize the damper. The nonlinear hysteretic biviscous model is used to identify four physical parameters of the MR damper from the force vs. velocity diagram due to sinusoidal input displacements: pre-yield damping, post-yield damping, yield force, and zero-force velocity intercept. The post- yield damping and the yield force are used to calculate effective MR fluid properties of plastic viscosity and dynamics yield stress, respectively, from the damper data. Using the effective dynamic yield stress and the effective plastic viscosity, the Bingham plastic model is used to predict the damping, and these predictions are correlated with measurements from the force vs. displacement hysteresis cycle. The damping coefficient is the ratio of the damping with the field ON, to the Newtonian damping associated with the plastic viscosity. The resulting damping coefficient vs. nondimensional plug thickness diagram successfully predicts the damping behavior of the MR damper.