Introduction: Reflective writing, a complex human activity is one of the innovative pedagogies to promote deep learning among medical students and doctors. Despite its potential to facilitate learning, there is limited literature on evaluation of various purposes of reflective writing in medical education. Hence, aim of this study is to develop an instrument and evaluate the perceptions of house officers about benefits of reflective writing. Methods: Mixed method study followed AMEE 87 guidelines for questionnaire development. The study was carried out from Oct 2018-Feb 2019 in a dental college in Islamabad. A 30-items questionnaire was developed by following these steps: (1) conduction of literature review, (2) item development, (3) conduction of cognitive interviews and (4) pilot testing. Coding and interpretation of transcribed data and notes taken during cognitive interviews was done to finalize three main themes (learning, self-regulation and alteration in clinical behavior) identified in literature review. In pilot testing, participants were asked to rate the purposes of reflective writing on a three-point Likert scale (Agree, do not know and disagree). Data was analyzed using SPSS version 22. Results: All of nineteen house officers (n= 3 for cognitive interviews, n= 16 for pilot testing) had previous experience of writing reflections using Gibb's reflective cycle. Thirteen (81%) out of sixteen house officers agreed that reflective writing improves learning, helps in self-regulation and alters clinical behavior, two (13%) did not know about the three themes that were finalized in cognitive interviews and one (6%) did not agree. Discussion and Conclusion: Reflective writing improves learning, helps in self-regulation and alters clinical behavior in the selected house officers. This study may inspire medical education experts to include reflective writing as a part of formal undergraduate medical and dental curriculum to enhance student's learning experience.