Abstract. The aim of the paper is the presentation of the main reasons of Tadeusz Kotarbiński's atheism and an interpretation of his position in terms of the conceptual apparatus used in contemporary philosophical debate on atheism. William Rowe distinguished three types of atheism: friendly atheism, indifferent atheism and unfriendly atheism, a divide widely accepted in contemporary debates. It seems that Kotarbiński's position is a form of unfriendly atheism. However, the final conclusion will be that William Rowe's conceptual apparatus is not a satisfying tool for an evaluation and interpretation of Tadeusz Kotarbiński's views.