This study examines, through experiments, two reinforced concrete girders obtained from a residential building constructed in 1961. The average concrete strength obtained from the material tests was approximately consistent with the specified strength. Honeycombs were observed in girders; hence, one of the girders was repaired using an epoxy resin injection to investigate the effect of retrofitting.The original and retrofitted girders were subjected to reverse loadings with displacement control and had a sectional area of 250 mm × 800 mm, according to the structural draft. Both girders were designed to exhibit a common shear span length of 1,200 mm to evaluate the validity of the current equations for shear capacity in seismic evaluation, as recommended in the criteria for seismic assessment in Japan. Using these equations, the ratio of the shear strength to flexural strength of the test girders was found to be 1.67. No significant difference was observed in the crack patterns of both girders. Their maximum strength reached the calculated flexural strengths; however, the shear cracks apparently progressed with the increase in drift angle. The hysteresis loops were slip-type because of the bond slippage of the main bars. The final failure mechanism was shear failure mode. The equation for flexural strength predicted the observed value of the original girder; the maximum strength of the retrofitted girder was approximately 1.1 times that of the original. Consequently, the epoxy resin injection recovered the seismic performance of the girders in this building.