: One way for evaluating the seismic Vulnerability of bridges is using the fragility curves. Indeed, these curves are useful tools for non-deterministic seismic performance assessment of the bridges before and after retrofit and are conditional probability of exceedence a damage level for a given ground motion intensity. Here in this thesis a probabilistic analysis by the use of developing fragility curves has been performed to investigate the influence of retrofitting with concrete jacketing method in reduction of vulnerability of the bridges. For developing these curves series of non-linear time history analysis with the use of 60 earthquake records before and after retrofit were performed and a statistic analysis were done on their results. Fragility curves has been indicated with the use of log-normal distribution functions with two parameters and based on the peak ground acceleration. The analytical method which has been used for developing fragility curves and also comparing them before and after retrofitting is indicated in this thesis. Comparing these curves shows us the significant reduction of vulnerability after retrofitting of columns with concrete jacketing. : One way for evaluating the seismic Vulnerability of bridges is using the fragility curves. Indeed, these curves are useful tools for non-deterministic seismic performance assessment of the bridges before and after retrofit and are conditional probability of exceedence a damage level for a given ground motion intensity. Here in this thesis a probabilistic analysis by the use of developing fragility curves has been performed to investigate the influence of retrofitting with concrete jacketing method in reduction of vulnerability of the bridges. For developing these curves series of non-linear time history analysis with the use of 60 earthquake records before and after retrofit were performed and a statistic analysis were done on their results. Fragility curves has been indicated with the use of log-normal distribution functions with two parameters and based on the peak ground acceleration. The analytical method which has been used for developing fragility curves and also comparing them before and after retrofitting is indicated in this thesis. Comparing these curves shows us the significant reduction of vulnerability after retrofitting of columns with concrete jacketing.