This qualitative study described the use of portfolio in College Biology as a tool to assess the professional growth of science and health teachers. Eight prospective elementary school teachers specializing in Health and Science at the Northern Iloilo Polytechnic State College, Estancia, Iloilo during school year 2002-2003 were purposely selected in this study. The students were engaged to make a portfolio on the unit in Ecology taken up for eight weeks as a part of the course. The portfolio, with all the entries and the corresponding rubrics, was the main data source and instrument of the study. Data from the portfolio was further enriched by information from FGD and informal conversations with the students. Findings of the study show that the process of portfolio making and the product called portfolio as a data source can provide product called portfolio as a data source can provide information that can reflect the professional and personal qualities of a prospective teacher. These qualities are labeled as professional growth. Likewise in the process of portfolio making, the students gained skills in various teaching methods. The construction of the rubrics for each entry has allowed the students to set standards for accomplishments and guided them as they prepared their portfolio entries. The reflections, as a meaning-making process, allowed the students to express their thoughts, feelings and actions. These have provided them experiences to make objective, evaluate and interpretive descriptions. Thus by all indications, a portfolio has a great potential and value as an alternative assessment tool for professional growth. These are reflected by the entries that indicate acquisition and development of knowledge, skills and attitudes as the students prepared for themselves to become science teachers.