In the article, considerations of the impact of surface preparation of glued machine parts on the mechanical strength of the adhesive connection are presented. The research was carried out on a number of cylindrical samples in the laboratory and samples made of steel sheet reflecting industrial conditions. The surface of the substrate was prepared in four different ways: sandblasting, degreasing, oil contamination of the surface and covering an area of glued parts of grease. The relationship between the mechanical strength of adhesive joint and contamination of the surface of bonded parts was defined, as a main result of the research.