The crystal and molecular structure studies of the mesogen, undecyloxybenzoic acid are reported. The compound(C18H28O3) crystallises in the triclinic space group P1 (1) over bar with a = 8.0495(10)Angstrom, b = 13.024(4)Angstrom, c = 4.7383(14)Angstrom, alpha = 92.97(3)degrees, beta = 102.910(14)degrees, gamma = 82.319(19)degrees. V = 848.1(3)Angstrom (3) Z = 2, D-(cal) = 1.145 Mg/m(3), mu = 0.076 mm(-1). F-000 = 320, GoF = 1.072, R1 = 0.071. It is shown that the phase transitions and physical properties of the mesogen are strongly dependent on the dimer formation.