This paper presents the effect of blade secular changes in stator and rotor blade passages on unsteady flows through the first-stage in a middle pressure steam turbine. The scales from the boilers may collide with the stator and rotor blade surfaces, and the blades could become gradually thinned or adhered over time because of the collision. The secular-changed blades influence the performance of steam turbines and may further induce unexpected accidents. Therefore, the maintenance, repair, and overhaul (MRO) of steam turbines is essential. The optimization of MRO scheduling is quite crucial for electric power companies. We simulated unsteady steam flows through an actual middle pressure steam turbine working at a coal-fired power plant while setting manufactured and secular-changed blades. The shape of the secular-changed blades was measured from actual blades during overhaul. The numerical method developed at Tohoku University was employed for the simulation. The difference in the results between the manufactured and secular-changed blades is shown, and the effect of secular changes on unsteady flows is investigated. In addition, the possibility of utilizing the results in the MRO of real turbines is highlighted.