It is difficult to characterize the shaft surface, which is the running surface of the radial lip seal, by only using the average roughness, Ra. Usually, roughness measurement instruments provide a lot of other parameters besides Ra. A discriminant analysis can be applied to these parameters with seal function tests. The discriminant function generated from roughness parameters in addition to Ra and the results from functional tests could be a useful tool to classify the preferred and non-preferred shaft surfaces for seal applications. The logic of the discriminant analysis is presented. The application of the discriminant function in shaft surface classification is discussed. A case study of a real application is given. The benefit and the limitation of the approach are also discussed.