Abstract: To evaluate the effects of corrosion and aftershock on structural seismic resistance. Two seismic designed reinforced-concrete frame buildings located in a coastal city were selected for study. Four corrosion conditions were considered, i.e., uncorroded and corrosion ratios of 5%, 10% and 15%. A set of 662 mainshock-aftershock sequences were taken as the inputs for time history analysis. Then the damage analysis and fragility assessment were conducted to the corroded and uncorroded buildings subjected to mainshock-aftershock sequences. Results show that the increment of corrosion ratio exacerbates structural cumulative damage under mainshock-aftershock sequences. The increment ratio of the structural cumulative damage is even over 30%. The corrosion effect can lead to an increase in fragility curves, and the influence of the corrosion effect on mainshock fragility curves under heavy corrosion condition is close to that under aftershocks. The coupling effect of corrosion and aftershock can cause a significant elevating in mainshock fragility curve. Therefore, it is necessary to consider the effect of corrosion in seismic performance assessment subjected to mainshock-aftershock sequences.