Presented article is an attempt to analyze Robert von Mohl’s views regarding the formal dimension of his rule of law idea (Rechtsstaat). In the first part, the article analyzes relations between the written law and customary law in the thought of discussed German scholar. Next it discusses the notion of constitution in state, also when it comes to its definitions. The article is finished by the issues of an act and an ordinance in von Mohl’s thought. Firstly it discusses the very notions of these normative acts. Secondly it analyzes the features that, according to von Mohl, should be fulfilled by them. Presented article proves not only the cohesion of von Mohl’s view in terms of rule of law’s formal dimension. It also proves that his views reflect the aspirations of German 19th century bourgeoisie. However, the article emphasize that von Mohl didn’t fully solve certain problems i.e. mutual relations between written and customary law.