The purpose of this study is to investigate and analyze the elements that influence on subject expertise in physical education of beginning elementary school teacher during their teacher socialization. In order to achieve the purpose mentioned above, multiple case study were set to observe four elementary school teachers whose teaching career were under five years were. Qualitative research methods with in-depth interviews, participant observation, and collection of documents were employed to collect data. The collected data were analyzed by using inductive categorical system and the data were conformed to be authentic by member check, peer debriefing and triangulation. The elements that influence on subject expertise in physical education, based on knowledge of objectives, knowledge of students\' understanding, knowledge of teaching strategies, and knowledge of curriculum., are listed below. First, research participants understood that the acquisition of motor skill and the pursuit of variable activities and pleasure are the objectives of physical education of elementary school. This understanding suggests that their positive and successful experience in sports participation had positively influenced in having confidence in their motor skill. In contrast the poor experience they encountered as students prompted them to create teaching environments different from above mentioned. For some, former teacher in elementary school influenced the development of teaching perspectives by providing teacher with a perspectives on both the pursuit of variety and pleasure. But for the most part the perspectives of elementary school education that regard variety and pleasure are the main elements that influence on knowledge of objectives. Second, on knowledge of students\' understanding subject, the research participants have understood that students most favor sports game while students don\'t like gymnastics. One can see that the fundamental reason which is related to their experience in physical education is that the negative experience in physical education enables them to understand the real reason of favor or disgusting in participating sports. Third, on knowledge of teaching strategies, the instruction pattern of all participants in this study is to explain main contents, show an example and feedback about the practice. and the principal elements that influence on this instruction pattern. It was found that these are so various and individually different. (e.g., Apprenticeship of observation, Teacher education and asking a colleague\'s opinion. In presenting of teaching tasks, most of tasks are presented by way of showing an skill example. And the apprenticeship of observation did appear to help teachers \"practice, analysis or master\" instructional skills that are necessary to perform various teaching tasks. In other words, many beginning teacher\'s experience in physical education were related to the contents of their instruction. Forth, on subject of knowledge of curriculums, the participants in this study collected materials for instruction through various methods (e.g., reference books, internet and asking colleague\'s opinion) and main reason of using material for instruction was because of the poor subject knowledge of their own. Again, poor experience in physical education and sports participation during their teacher socialization are compounded and mixed and as result, these helped to form their knowledge of curriculums. For some, self confidence that is formed by positive and successful experience in sports participation makes a teacher who doesn\'t need or require any additional materials for the proper instruction.