Abstract: Aftershock has a significant influence on the seismic risk of engineering structures. To evaluate the seismic risk subjected to mainshock-aftershock scenario, this study develops a framework for seismic risk estimation considering the contribution of aftershock. The proposed framework divided the risk estimation into two parts, namely the mainshock-aftershock fragility analysis and mainshock-aftershock hazard analysis. For the fragility assessment, the total probability theorem is adopted to couple the mainshock- and aftershock- fragility functions, which are developed upon the displacement-based fragility formula. For the seismic hazard analysis, the copula technique is used to generate the conditional distribution of aftershock intensity. Based on an improved “indirect approach”, a vector valued mainshock-aftershock hazard function is obtained in conjunction with the mainshock hazard curve and the obtained conditional probability. The seismic risk function is developed by combining the fragility and hazard functions. To illustrate the framework proposed, a seismic-designed RC frame building is employed as the case structure. The seismic risks are discussed for the case structure during its service life. Analysis results show that the seismic risk under mainshock-aftershock sequence is approximately twice as that under mainshock only. The seismic risk for all limit states raises with the increasing of the service time. When the service time is 40 years, the collapse risk under mainshock-aftershock sequence reaches to 69 times of the initial structure under mainshock only. The effect of the aftershock cannot be ignored in the structural seismic risk assessment of buildings.