One of the most important vibration isolators in vehicles is the powertrain mounting system (PMS). It transmits the powertrain vibrations to the body, and the chassis vibrations excited by road to the powertrain. The design of a PMS is an essential part in vehicle safety and in improving the vehicle noise, vibration and harshness (NVH) performances. Many organizations are increasingly relying on design simulation rather than trail-and-error based experiments which are expensive and time-consuming for PMS evaluation. However, design parameters for PMS are always uncertain in actual cases due to tolerances in manufacturing and assembly processes. In this paper, based on a front wheel drive vehicle with a transversely four-cylinder engine, the uncertain characteristics of PMS are studied by interval analysis method. Considering the design parameters including locations, orientations and stiffness of the mounts as interval variables, the lower bounds, upper bounds of natural frequencies and the mode kinetic energy distributions of a PMS are estimated by means of interval analysis. Moreover, the first order analytical design sensitivities are derived to choose the more effective parameters. The response surface methodology (RSM) based on design of experiment (DOE) is investigated to obtain the exact expressions of natural frequencies and kinetic energy distributions. For comparison, a Monte Carlo simulation with normal distribution is used to illustrate the confidence and validity of the proposed method.