“The view of the teacher toward the nature of science is a major factor in determining the way that science teachers present material to students”. This statement could be sufficient by itself to justify the attention paid to epistemology in science teacher education. Thus, in recent literature there is a general consensus about the necessity of explicitly addressing this theme as central to any systematic approach to teacher preparation to teach. In addition to this mentioned consensus, there is a general concern about the content knowledge displayed by teachers when explaining the subject matters in class. In the last International Handbook of Science Education, several chapters deepen on this issue pointing out possible causes for these anomalous facts. In some meta-analysis studies of the literature about teacher education, the teachers’ content knowledge, together with the didactical content knowledge (or pedagogical content knowledge) focus the main conclusion of the researchers. In our opinion, there is another important point, which is lacking in these analyses, namely, the ontological aspect of the subject matter content. This is directly related to the critical thinking of the teacher about what is the nature of the entities constructed by science to explain “facts”, laws and theories. And these aspects, according to the revised literature, are those that most affect the live relationship between teachers and learners in science class. It seems as if the “epistemological framework” were too big grain analysis to give account of the “scientific behaviour” of the teachers in classroom settings. In this lecture we will try to shed light into these aspects of teacher education, stressing the necessity of introducing ontology into the systematic preparation of teachers training courses.