The influence of the terminal substituent of azobenzene on the liquid crystalline property of ABA triblock copolymers was studied. Three kinds of azobenzene-containing monomers with different terminal substituents were respectively used to synthesize ABA triblock copolymers (denoted as PMMAzo12-PEG13-PMMAzo12, PEMAzo14-PEG13-PEMAzo14, and PNMAzo14-PEG13-PNMAzo14) by atom transfer radical polymerization (ATRP). These copolymers were characterized with 1H NMR and GPC, and exhibited controlled molecular weights and narrow molecular weight distributions. Differential scanning calorimetry (DSC) and polarizing optical microscopy (POM) have shown that these copolymers have mesophases. PMMAzo12-PEG13-PMMAzo12 has a smectic mesophase and a nematic mesophase, while both PEMAzo14-PEG13-PEMAzo14 and PNMAzo14-PEG13-PNMAzo14 have a nematic mesophase. This demonstrates that the LC properties of these copolymers highly depend on the terminal substituent of azobenzene.