The unsteady lifting surface theory for a model composed of five bladerows is developed to predict unsteady aerodynamic forces on oscillating blades of aerodynamically coupled multistage annular bladerows. The theory is formulated to calculate generalized aerodynamic forces which appear in Lagrange’s equations of blade motions, so that it can be used as the aerodynamic tool for the inter-row coupling flutter analysis of multistage bladerows. Numerical studies were also conducted to investigate the mutual aerodynamic influences among bladerows. The simultaneous effects of co-rotating upstream and downstream bladerows located at next to the next position significantly modify the aerodynamic response of oscillating blades. The aerodynamic force induced by the oscillating bladerow is not very small even on the bladerows remoter than the next-to-the-next bladerow.