Phase situation of didodecyldimethylammonium bromide (DDAB) was investigated by means of differential scanning calorimetry, X-Ray diffraction and optical microscopy methods. A complex polymorphism was detected. Apart from the crystalline phase on hearing there are two liquid crystalline phases below the isotropic liquid and on cooling a third phase appears. The study shows that DDAB exhibits highly ordered layered liquid crystalline structures. The high-temperature phase which appears below the isotropic phase can he identified as SmB phase. The influence of thermal history the polymorphism of DDAB was studied. The enthalpy changes at the transitions were calculated.