Underground pipelines play an essential and indispensable role in a nation’s economy, prosperity, health, environment, social well-being and quality of life. As such they are often referred to as lifeline of the society. However, buried pipelines can be fragile when they are subjected to various mechanical and environmental actions. Of many such actions, seismic actions, i.e., earthquakes, are of most concern. There is thus a clear need to investigate the fragility of buried pipelines under the attacks of seismic actions. Moreover, seismic fragility analysis is an integrated part in the lifecycle management of pipelines. This paper proposes a probabilistic method for determining the seismic fragility of buried pipelines considering the uncertainties in the occurrence and intensities of seismic actions. In this method, the ground motions are first generated using the well-established random function-spectrum representation model (RFSRM). Then the dynamic responses of pipelines are simulated based on nonlinear dynamic analyses with varying levels of peak ground acceleration (PGA). By repeating the above two steps, the statistics of the dynamic responses of the pipeline can be obtained and so is its probability distribution function. With a given acceptable limit of the dynamic response, a limit state function can be constructed and then the probability of failure due to seismic actions can be obtained using existing structural reliability method. With different acceptable limit, a fragility curve can be plotted for different PGAs. A worked example will be presented to demonstrate the application of the proposed method and its accuracy and efficiency. The significance of the paper is that seismic fragility analysis provides a scientific basis for pipeline design, operation, maintenance, and risk management in their whole life.