Atomic force microscopy was used to study the surfaces of oxygen-plasma-treated polypropylene (PP), kraft pulp, filter paper, and wood. The effect of plasma treatment on the adhesion properties between PP film and wood was evaluated by means of a peel test. The highest adhesion to wood resulted from the shortest treatment times used. The effects of plasma on the adhesion properties were more pronounced when both the PP film and the wood surface were treated. Oxygen plasma caused changes in the morphology of the materials: the treated PP surface was covered by a nodular structure, which was not seen on the untreated film. A similar nodular structure was also seen on the lignocellulosic materials. These nodules seemed to have poor interaction with the PP surface, resulting in a weak interface between the plastic film and wood.