This paper presents the fundamental seismic response and analytical idealization in the substation steel structures. To obtain realistic response, the seismic observation was conducted on the steel structures which were under operation. The spectral analysis, as well as the dynamic response analysis, was performed in evaluation of the observed records. It was found that the in-plane response in the two-dimensional frame structures was less affected by the electric wires, but the out-plane response became complicated due to the effect of the electric wires such that the detailed model of the wires was required in the analysis. On the other hand, the correlation between observation and simulation in the three-dimensional frame structure could be improved by increasing the damping ratio without modeling of the wires.