本研究的主要目的有二，第一是探究一位擁有四年教學經驗的國小自然科教師，其原有的教師信念與教學實務。第二是經歷本研究所設計的教師專業成長活動後，其教師信念與教學實務的改變歷程。從文獻整理中發現，對於影響教師實施建構主義取向教學的信念，可分成下列三個信念組：一、過去經驗的信念組。二、環境文化的信念組。三、知識論的信念組。研究結果發現：一、由建構主義的觀點來看，學期初個案教師這三個信念組均呈現不同於建構教學的信念，而個案教師的教學實務則普遍採取教師為中心的教學方式。二、透過知識論為基礎的專業成長活動，將可能有助於個案教師建構建構主義的相關知識背景，使研究者與個案教師更容易溝通，並可協助個案教師進行自我反思。三、學生良好的回饋有助於建立新成功的教學經驗，改變過去經驗的信念組的，使教師對於實施建構主義取向教學有安全感與滿足感，進而挑戰舊有環境文化與知識論的信念組。文末亦根據研究結果對當前師資培育、課程推廣與後續研究提出建議。

This paper explores the transformations in the beliefs and practices of a primary school teacher of science in the context of participation in constructivist-based professional development. This case study research employed formal and informal teacher interviews and the qualitative instrument “Secondary Teaching Analysis Matrix ⎯ Science Version” (STAM). The research aimed to authentically describe the transformations of the teacher’s beliefs and practices. Constructivist li-terature suggests that a teacher core belief system can be separated into three belief sets, past experience belief sets, environment and culture belief sets, and epistemology belief sets. The results from this study are threefold. First, the teacher’s three belief sets did not initially include beliefs about the importance of a constructivist approach. This was manifest in a teacher-centered approach in the initial semester. Second, employing a constructivist approach assisted the teacher to change the original belief sets. Third, the positive response of students assisted the teacher to shift his practice from teacher-centered to student-centered. This study suggests that discussions about epistemology during teacher professional development may assist teachers to realize a constructivist approach in their teaching. Further studies of teacher belief sets may be warranted.