Disclosed is a method for improving the barrier properties of polyethylene films. The method comprises mixing a substantially linear, high density polyethylene with a nucleating agent and converting the mixture into a film. The film made by the method of the invention has at least a 15% improvement on the water vapor barrier property and/or in the oxygen barrier property compared with the control film made from the same substantially linear, high density polyethylene but does not contain the nucleating agent.