The purpose of this research is to analyze the life and earth science curricula in Tunisia in order to determine its characteristics and to know if it really helps to develop critical thinking as it is claimed in curriculum documents. In this analysis, the authors applied the revised Bloom's taxonomy. The results show that curriculum authors ignore the more complex cognitive processes and the most abstract knowledge, which leads to imagine that there is a barrier to encountering the higher levels which makes it impossible to develop critical thinking among students.