Amphiphilic molecules self-assemble into supramolecular structures of various sizes and morphologies depending on their molecular packing and external factors. Transformations between various self-assembled morphologies are a matter of great fundamental interest. Recently, we reported the discovery of a novel class of single-chain galactopyranosylamide amphiphiles that self-assemble to form vesicles in water. Her; we describe how the vesicles composed of the amphiphile N-oleoyl beta-D-galactopyranosylamine (GOA) undergo a morphological transition to fibers consisting of mainly flat sheet-like structures. Moreover, we show that this transformation is reversible in a temperature-dependent manner. We used several optical microscopy and electron microscopy techniques, circular dichroism spectroscopy, small-angle X-ray scattering, and differential scanning calorimetry, to fully investigate and characterize the morphological transformations of GOA and provide a structural basis for such phenomena. These studies provide significant molecular insight into the structural polymorphism of sugar-based amphiphiles and foresee future applications in rational design of self-assembled materials.