A series of methylene-linked symmetrical liquid crystal dimers were synthesized. Their structures were confirmed by physicochemical techniques. Differential scanning calorimetry and polarizing optical microscopy verified the liquid crystal behaviors and their transition temperatures. The thermodynamic data for phase transition, melting transition (T-m), and isotropic transition temperatures (T-i) of the dimers were decreased with increasing the length of spacer. Both T-m and T-i and enthalpy change for isotropic transition (delta H-i) for dimers with even numbers of methylene units were higher than those with odd numbers. Dimers AC-OnO-AC (n = 2-10) formed enantiotropic nematic phase only, while the unsymmetrical dimer formed a smectic phase.