The self-efficacy of prospective primary teachers was studied, considering in particular the relationship of that construct with the emotions they expect to experience as future science teachers, differentiating between when they will be teaching the content of the "nature sciences" (biology and geology) and that of the "hard sciences" (physics and chemistry). The study instrument was a questionnaire completed by 188 prospective primary school teachers in their initial education at the University of Extremadura during the academic year 2009/2010. The results showed them to mostly have positive emotions towards nature sciences and negative towards the hard sciences. While their beliefs concerning their self-efficacy are significantly related to their emotions about their future teaching of the hard sciences, high self-efficacy was significantly correlated with more positive emotions and fewer negative emotions towards physics and chemistry. (Contains 2 tables and 7 figures.)