Metallic sandwich panels with rock wool core (MSPRWC) are widely used in long-span roof structures. The weak rigidity and damping property of MSPRWC can change the characteristics of fluctuating wind pressure acting on the roof, and even have substantial effects on the dynamic response of structural wind-induced vibration. However, it is seldom considered in practical structural design. Some basic mechanical parameters of the rock wool material, including its tensile and compressive strength, elastic modulus and Poisson’s ratio, are tested. The damping property of the rock wool was measured by the vibrating beam method, and the loss factor-frequency curve of rock wool material is fitted according to the testing results. Further, modal strain energy method was employed to calculate the modal loss factor of a 0.4m×2m MSPRWS with typical span. The results reveal that the modal loss factor of MSPRWS can reach as high as 0.5, the minimal loss factor of those main modes perpendicular to the roof panel even approaches 0.2. It indicates that damping properties of MSPRWC cannot be neglected for the analysis of structural wind-induced vibration.