The effect of ultraviolet (UV) radiation of lambda greater than or equal to 250 nm on the thermal stability, electrical and optical properties of thin poly-para-xylylene (parylene) thin films was studied. Evidence of slight oxidation of the UV treated film was seen using Fourier-transform infrared spectroscopy. Thermal desorption spectrometry and thickness change after annealing were used to analyze the thermal stability of as-deposited and UV-treated parylene thin films. The thermal stability of the UV treated films was seen to decease as the radiation dose increased. Electrical measurements revealed an increase in the leakage current density, the dielectric constant and the dissipation factor of UV treated films. No change was seen in the refractive index at 634 mn.