In this paper, growth behavior of high density Al2O3 which was prepared by using cyclic chemical vapor deposition (C-CVD) system has been systematically investigated. Tri-Methyl-Aluminum (TMA) and oxygen (02) plasma was used as source precursor and reactant, respectively. Unlike the conventional ALD system that source precursor and reactant was injected alternatively that was separated by inert gas purge step, TMA and 02 was mixed and co-fed into the process chamber simultaneously, followed by purge step. To obtain high density and defects-free Al2O3 layer, source precursor feeding time and the number of deposition cycles dependence on the thickness of C-CVD grown Al2O3 layer were investigated. We found that thickness of Al2O3 layer was increased almost linearly as the number of cycles increased which are typical characteristics of CVD. On the other hand, self-limiting phenomenon was observed in thickness as source feeding time increased which showed saturation of the thickness as source feeding time further increased. Using the optimized C-CVD process conditions, density of 3.298 g/cm3 was obtained in 100 nm thick Al2O3 layer whereas that of ALD Al2O3 was 3.192 g/cm3. The C-CVD grown Al2O3 layer effectively prevents water vapor from diffusing into active layer of organic light emitting diodes, which shows C-CVD grown Al2O3 layer can be applied to water vapor permeation barrier layer in organic light emitting diodes.