A series of catanionic surfactants were prepared by making an equimolar mixture of cationic (alkylammonium chloride) and anionic(sodium alkyl sulfate) surfactants, both containing an isomer of the same chain length, namely, C-10, C-12, or C-14 The prepared compounds exhibited complex thermal behavior, characterized by several successive phase transitions in the solid state as proved by differential scanning calorimetry, X-ray diffraction, and optical birefringence observation using a polarizing microscope. On heating, three main phase transitions were observed for all compounds; solid crystalline-solid crystalline, solid crystalline-liquid crystalline, and liquid crystalline-isotropic liquid. On cooling, all three compounds underwent reversibly the isotropic liquid-liquid crystalline phase transition, while the liquid crystalline-solid crystalline phase transition displayed peculiar properties. Phase transition temperatures increased with an increase in hydrocarbon chain length.