The synthesis and some thermal properties of a new type of block copolymers comprising both main-chain and side-chain liquid-crystalline (LC) blocks in the same macromolecular structure are described. The former block is a semiflexible LC polyester (block A), and the latter is a LC polymethacrylate (block B). The two structurally different blocks were at least partly phase-separated within the glassy and LC states and underwent distinct phase transitions. Significant deviations of the thermodynamic parameters observed relative to those of the corresponding homopolymers suggest the occurrence of a more or less diffuse interphase.