The hexanitrates of the six-carbon sugars mannitol and sorbitol were prepared and studied to gain insight in their relative stabilities. Synthesis and characterization of these materials resulted in the identification of two new crystalline polymorphs, one for each hexanitrate. Mannitol hexanitrate (MHN) exposed to elevated temperatures exhibited a different structure when measured by x-ray diffraction (XRD) and Raman spectroscopy; however, no differences were observed in the thermal behavior. Sorbitol hexanitrate (SHN) has two distinct crystalline polymorphs that result in different melting behavior and differences in Raman and XRD. Thermal stability of these hexanitrates was also examined; despite being isomers, SHN and MHN differ in their long-term thermal stability.