Lotus-type porous magnesium was fabricated by unidirectional solidification of the melt dissolving hydrogen in a high-pressure mixture gas of hydrogen and argon. The damping constant a of porous magnesium with various porosities was measured by the hanging excitation method. The damping constant was defined as alpha=109 (x(n)/x(n+1))/Delta T, where x(n) and x(n+1) are the successive amplitude values of the damping wave, and Delta T is the damping time. The frequency-amplitude dependence curve was obtained by Fast Fourier Transform analysis. The damping time of the lotus-type porous magnesium was observed to be shortened greatly compared with non-porous metals and porous copper. Moreover, the damping constant of the lotus-type porous magnesium was calculated by the damping amplitude.