A thermotropic copolyester I-19 prepared from a rigid, bent spirobicromane (SPI), 1,7-heptanediol (HD), and an aromatic ester triad, TOBC (terephthaloyl bis(4-oxybenzoyl chloride), was prepared and its thermal behavior investigated by differential scanning calorimetry. Copolyester I-19 exhibited completely different DSC thermograms between samples cooled from the isotropic liquid and the mesomorphic states, a result attributable to the registry effect of the neighboring chains in the mesophase. Non-isothermal crystallization at different cooling/heating rates, and isothermal crystallization and annealing at various temperatures had been conducted to verify the origins of the complicated four melting endotherms (as Tm1, Tm2, Tm3 and Tm4 from high- to low-temperature regions) in the sample cooled from the mesomorphic state. The highest-temperature Tm1 transition is attributed to the melting of the primary crystal formed via the liquid crystalline nuclei. Tm2 and Tm3 transitions are due to melting of the less perfect, secondary crystals close and less close to the pure crystals responsible for the Tm1 transition. By choosing suitable isothermal crystallization and annealing processes, Tm2 and Tm3 transitions can be moved to merge with Tm1 to become one high-temperature single melting endotherm. The lowest-temperature Tm4 transition, which basically remained intact after different thermal treatments, is caused by the melting of the chain segments near the SPI moieties.