This study proposes a monitoring method for corrosion on reinforced concrete structure using inverse analysis approach. At first, we define an inverse problem to identify the real and imaginary parts of the concrete conductivity and the impedance between concrete and steel. The observation of the inverse problem is the electric potential on the concrete structure surface when the AC impedance measurement is performed. The observation condition, such as layout of observation point and type of observation, of the inverse is optimized. The optimization is achieved by minimizing the average of eigen values of a posteriori estimate error covariance matrix based on the Kalman Filter estimation algorithm. We show a numerical simulation to solve the inverse problem on the optimized observation condition to evaluate the effectiveness of the condition. The simulation shows the real parts of the concrete conductivity and the impedance are well identified but imaginary parts of them are not. To overcome this difficulty, we evaluate the sensitivity of the imaginary part of the impedance to the real part and the imaginary part of the electric potential. We find the possibility that the observation of the imaginary part of the electric potential improves the estimation. Finally, a numerical simulation is performed under the optimized observation condition considering the above discussion. In the numerical simulation shows that considering the sensitivity of the parameters to the potential improves the solution on the inverse problem.