In the past decades, barrier polymer packaging has received much attention especially in the food packaging industry. The addition of solid nanoparticles to polymer matrices is a well-known known approach to achieve high barrier polymer films. Among different nanoparticles, nanoclay sheets have been shown to be the most efficient particles in improving gas barrier properties. In this work, gas barrier properties of nanocomposite films prepared by melt mixing and nanocomposite coating were investigated. In the melt mixing approach, the effect of dispersion and nanoclay content on oxygen barrier properties of polypropylene-grafted-maleic anhydride (PP-g-MA)/nanoclay films was examined. It was found that the addition of 2 wt.% of nanoclay reduced oxygen permeability by more than 50%. X-ray diffraction results and rheological analysis confirmed a well-dispersion of nanoclay in PP-g-MA matrix. The mechanisms involved in improving oxygen barrier properties were discussed in detail. In the second approach, nanocomposite coatings mainly based on Montmorillonite and Chitosan were applied on the surface of a PET film using the layer by layer (LbL) deposition technique. The LbL technique was adopted in order to reach a high percentage of 60 wt.% nanoclay in the coating which allowed a significant reduction of 98.69% in oxygen permeability. In addition, the effect of nanoclay orientation and dispersion as well as polymers’ interaction on oxygen barrier properties were studied.