Abstract The free vibration analysis of rotating polar orthotropic sandwich annular plate with electrorheological (ER) fluid core layer is studied in this study. By using discrete layer annular finite element method, the equation of motion for the rotating polar orthotropic sandwich system is derived. The ER fluid is utilized to control the vibration and damping characteristics of the rotating polar orthotropic sandwich annular plate system. Additionally, the extensional and shear modulus of ER fluid are described by complex quantities. And, the natural frequencies and loss factors of the system are obtained by solving the complex eigenvalues of the system. Natural frequency and modal loss of the rotating polar orthotropic sandwich annular plate with different designed parameters are calculated and discussed in this study.