In this study, parylene-C films were deposited using vertically aligned-chemical vapor condensation (CVC) method and effects of post-annealing were investigated. The comparison results for as-deposited and post-annealed samples showed that the structural properties changed gradually with varying annealing temperature, while optical properties and surface morphology of the films seldom changed. The crystallinity, crystallite size, and d-spacing were changed from 60 to 87.2%, from 6.83 to 15.6nm, and from 6.41 to 6.26 angstrom, respectively. The value of oxygen transmission rate (OTR) for the films was changed gradually from 3.22 to 1.53 cc/m(2)center dot day after annealing process. However, the values of transmittance and surface roughness were 90% in the visible-near IR region and 5nm without reference to annealing temperature. Consequently, the crystallization of parylene-C films was one of major effects without the change of optical properties and surface morphology after annealing process, and we believed that the enhancement of crystallinity caused to improve the property of OTR for parylene-C films.