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 of porous magnesium with various porosities was measured by the hanging excitation method. The damping constant was defined as α=log (xn/xn+1)/T, where xn and xn+1 are the successive amplitude values of the damping wave, and 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.