Liquid crystalline compound 4-n-(decyloxy) benzoic acid has been irradiated by Li ion beam in its crystalline phase at room temperature by a pelletron beam using 3nA current. Thermodynamic, dielectric and UV–Visible spectroscopic characterization of the pure and irradiated materials has been carried out. Thermodynamical studies of the pure and irradiated materials show that all the transition temperatures, enthalpies and hence entropies are increased due to the irradiation suggesting enhancement in the thermal stability of the mesophases. Dielectric results obtained on the irradiated vis-à-vis pure material suggest how the value of the transverse component of the dielectric permittivity of the irradiated material increases in the SmC phase whereas it decreases in the N phase as compared to that of the pure material. UV–Visible spectrum of the irradiated material shows an additional peak along with the peak of the pure material suggesting formation of new species in the irradiated materials.