A series of new triphenylene discotic liquid crystals has been synthesized by a straightway and the influence of molecular symmetry and chain length on the mesomorphism investigated. The symmetrical compounds 1, 3,7,11-trimethoxytriphenylene-2,6,10-triyl tris(3,4,5-tris(alkyloxy)benzoate), with alkyl chain lengths of C7, C8, C10, and C12, and the unsymmetrical compounds 2 were studied by using polarized optical microscopy (POM), differential scanning calorimetry (DSC) and by wide-angle X-ray diffraction (XRD). The results showed that the symmetrical compounds 1a (C7) and 1b (C8) exhibit a plastic columnar mesophase, whereas the other compounds display a hexagonal columnar mesophase over a wide temperature range. All symmetrical compounds 1 display higher isotropization temperatures than that of the unsymmetrical 2. The clearing points are lowered as the alkyl chain lengthened.