Formulae of hysteresis characteristics of steel reinforced concrete (SRC) beam-columns under earthquake loading were proposed in order to develop rational and reliable structural design. Elastic-plastic behavior of SRC beam-columns was affected by a lot of factors, such as axial load ratio against axial compressive strength of SRC cross section,@dimension of encas ed steel, strength of materials and hoop ratio. And these factors are complicated and have made to difficult to evaluate quantitatively@the hyste resis characteristics of SRC beam-columns. An experimental work of SRC beam-columns under constant axial load and cyclic horizontal load was carried out in order to investigate the elastic-plastic behavior of SRC beam-columns, and to make clear the effect of axial load ratio and shear span ratio on the hysteresis characteristics of SRC beam-columns. And also a numerical analysis of beam-columns was carried out with a cantilever model consisted of rigid part and elastic-plastic hinge at the column base, by calculating of moment and curvature relationship of the cross section at the elastic-plastic hinge. In this paper results of the experimental work and the numerical analysis were discussed and it was showed that the elastic-plastic behavior obtained by performing the analysis agreed well the experimental results. And it was showed that elastic-plastic behaviors of SRC columns under earthquake loading were evaluated well by skeleton curves consisted of the straight lines connecting the following four points; happening point of transverse tension crack of concrete, flexural yielding point, point of achieving maximum strength and point of strength deteriorating. And these four points on the skeleton curves are affected by axial load ratio, dimension of encased steel, strength of materials and hoop ratio. Then it was investigated quantitatively by performing analysis how difference of those factors effects on the elastic-plastic behavior and the skeleton curves of SRC beam-columns encased simple H-shaped steel under earthquake loading. And formulae of hysteresis characteristic of SRC columns were proposed, by performing the statistical researches on the strength and the deformation of the four points on the skeleton curves affected by the several factors. The proposed formulae estimated well the elastic-plastic behaviors obtained by carrying out experimental works of beam-columns.