Abstract: The inelastic displacement ratio spectra is an effective way to estimate the maximum lateral inelastic displacement of structures. The inelastic displacement ratio spectra for reinforced concrete regular frame structures is investigated based on the structures designed with Chinese code for design of buildings. It is concluded that the trend of inelastic displacement ratio spectra for frame structures is similar to that for single-degree-of-freedom (SDOF) systems. In short period range (about shorter than 1.2s), the inelastic displacement ratio spectra for frame structures dramatically decrease as the periods increase, and the spectra tend to be a constant for periods longer than 1.2s. It should be pointed out that in the long period range especially for higher ductility, the equal-displacement rule will not be adoptable since the spectra are much larger than 1.0. In order to estimate the maximum lateral inelastic displacement of frame structures by the inelastic displacement ratio spectra for SDOF systems, the modification factors of inelastic displacement ratio spectra for SDOF systems are also presented.