Most of the studies conducted on the design of inflated fabric structures for space applications have focused on types of yarns and coating selection. The design of seams along with materials selection considerations is also crucial to the design of inflatable structures. This paper presents a pilot study of the modes of failure for fabrics with two selected sewn seams under biaxial stress loading. A literature review of sewn seam testing techniques reveals that conventional methods do not accurately simulate the biaxial stresses to which inflated fabrics are subjected. In this study, biaxial stresses are obtained by using a cylindrical pressure testing apparatus developed originally for testing seam design for an inflatable Lunar habitat. The unique features of the test method for sewn seams of fabrics by cylindrical pressure loading are described. Test data is presented, and the sensitivity of the test to changes is also discussed.