Although proponents support portfolios' value to enhance the reflective thinking of novice teachers and imply that such thinking improves teachers' practice, few studies have confirmed these assertions by directly measuring in-depth reflection or describing conditions that develop it. In this study, reflective thinking in preservice teachers' portfolios was measured and compared with their perceived reflection. Qualitative research design was used for this study. The participants were preservice physics teachers. Data were collected through the participants' portfolios and interviews. Their portfolios were evaluated based on the rubric developed by the researcher focusing on personal reflection, artifacts, professional development, and organization. Findings show that most of the preservice teachers gained expertise in reflecting about their teaching skills in their portfolios. These findings also indicate that the instructor's supervision and help throughout portfolio preparation may have assisted the preservice teachers with creating more reflective portfolios.