Science teachers' competencies are analyzed in this paper. The importance of teachers' competencies is underlined and also the importance of competencies in so called "good practices" obtaining, is studied. The definition of science teachers competencies and their taxonomy are very important in understanding the educational reform in European context. The recent literature and many reforms in the field of science teacher education suggest that teacher preparation has a "threefold structure" with the anchoring pillars being Subject Matter Knowledge (SMK), Pedagogical Knowledge (PK) and Pedagogical Content Knowledge (PCK). Science education programs should pay more attention into the learning of science in social and technological context. The reform in the educational field has to pay a special attention on science teachers' competencies.