The purpose of this study is to search the essence and factors of the kindergarten teachers' Pedagogical Content Knowledge (PCK) in science teaching and to develop the assessment tools of kindergarten teachers' PCK in science teaching. The questions of this study are as follows. 1. How are items of developed assessment tools constructed? 2. Are the assessment tools reliable? 3. Are the assessment tools valid? Firstly, based on the reviews of relevant literatures, pre-research was carried out to search for the essence and factors of the kindergarten teachers' PCK in science teaching, followed by development of the appropriate items for each factors. Among the developed fifty items in five factors, forty four items in were selected after content validity assessment. Secondly, as the first research, the questionnaire survey that was developed by the pre-research was conducted with 308 inservice kindergarten teachers. The reliability of each factor in the items of the initial development has been analysed by Cronbach α and the Item-Scale Score Correlation. Factor analysis for construct validity has also been carried out. Following the second request of content validity after correcting the procedure based on the first research, forty eight items in five factors have been confirmed for reconstructing the questionnaire. Thirdly, the questionnaire survey that was reconstructed by the first research, has been conducted with 502 inservice kindergarten teachers for the second research. Following the request of construct validity for the reliability verification and confirmative factor analysis, forty six items in five factors were eventually developed and confirmed for the final questionnaire. Finally, for the verification of the forty six items in five factors of the final assessment tools that were development through the first and second research, reliability and construct validity have been examined. It is concluded that the kindergarten teachers' PCK in science teaching consists of five factors: teacher's knowledge of curriculum, teacher's knowledge of students, teacher's knowledge of instruction, teacher's knowledge of contents, and teacher's knowledge of professionalism. Those five factors are in high correlations between each other. Secondly, the assessment tools developed by the research is highly reliable and thus is suitable for assessing kindergarten teachers' PCK in science teaching.