Kazimierz Twardowski is the father of the modern Polish analytical philosophy. One of the most important stamp of this philosophical style is referring - in philosophical investigations - to achievements and methods of natural sciences. The article analyses this plot in Kazimierz Twardowski’s philosophical works. It contains, in particular, a reconstruction of Twardowski’s views concerning the classification of sciences, the methodological status of philosophy and psychology and the mind-body problem. Some not commonly known facts concerning the sources of Twardowski’s interests in philosophy and science are mentioned.