© 2019 JSME. Piezoelectric shunt damping is a technique for vibration suppression by connecting an external circuit called the shunt circuit to a piezoelectric element attached to a mechanical structure. Many previous studies consider only a single mode for designing shunt circuits. However, the vibration of actual structures typically includes multiple vibration modes. It is consequently necessary to consider multiple modes toward designing a high-performance vibration control system. This paper proposes a method for estimating multiple-mode parameters of a piezoelectric structure, which is composed of a piezoelectric element and a flexible structure. The proposed multiple-mode parameter estimation method is derived by expanding a previously proposed method for single-mode parameter estimation. The effectiveness of the proposed estimation method is verified by experiments.