Relating to the design of liquid-metal blankets in a fusion reactor, numerical calculations have been performed on liquid-metal magnetohydrodynamic (MHD) flows in rectangular ducts with sudden expansions. Conservation equations of fluid mass and fluid momentum, together with the Poisson equation for electrical potential, have been solved numerically. The numerical calculations have been performed for Hartmann (Ha) numbers up to the order of 10000 and expansion ratios up to 4. The pressure loss through the expansion has been estimated by the loss coefficient ζ divided by the interaction parameter N, i.e., ζ/N. The loss coefficient ζ/N through the expansion parallel to the magnetic field is much larger than that through the expansion perpendicular to the magnetic field. The loss coefficient ζ/N increases consistently with the expansion ratio. The loss coefficient ζ/N does not change very much with the interaction parameter N and the wall conductance ratio.