This paper aims to explore an Indonesian prospective mathematics teacher's lesson planning and identify its characteristics of mathematical task design from the viewpoint of the anthropological theory of the didactic. The well-documented activities concerning lesson planning developed by the prospective mathematics teacher in her experiment to conduct a study on mathematics teaching were used as the primary data to be analyzed. Part of the anthropological theory of the didactic, namely mathematical praxeology, was used as the theoretical framework to analyze and explore the mathematical tasks design, their techniques, theoretical arguments of the techniques used, and theories underpinning the theoretical discourses. The study points out mathematical praxeology for each mathematical task included in the lesson plan analyzed. In addition, this study also figured out the characteristics of the mathematical praxeology of the lesson design developed by the prospective teacher.