The effect of working pressure on the properties of Al2O3 films was investigated in direct-type plasma-enhanced atomic layer deposition. Increasing pressure yielded a denser Al2O3 film and a thinner SiOx interlayer, but only slightly affected the Al2O3 film thickness. The diffusivity of O atoms was evaluated by using time-averaged emission intensities of the He I and O I lines. The consumption rate of O radicals and the production rate of H radicals, as functions of plasma exposure time, were deduced from analyzing temporal evolutions of emission intensities of the O I and H-alpha lines, respectively. The amounts of C and H impurities in the film were confirmed by using an X-ray photoelectron spectroscopy. Finally, the mechanisms by which the working pressure affected the properties of Al2O3 films were discussed based on the experimental results.