A binary mixture of cholesteryl ethyl corbonate (CEC) and terephthal-bis-p-n-tetradecylaniline (T-B14A) exhibits a twisted grain boundary (TGB) phase and smectic polymorphic phases. The mixture exhibits TGB-A and TGB-C phases at different concentrations and at different temperatures. Mixtures with higher concentrations of T-B14A exhibit I - Ch - TGB-A - TGB-C - Sm A - Sm I - Sm F phases sequentially when the specimen is cooled from its isotropic melt. The existence of different TGB phases and polymorphic smectic phases are confirmed by differential scanning calorimetric (DSC) and optical microscopic studies. The phase diagram is in accordance with the Renn and Lubbensky model.