Purpose: The purpose of this paper is to introduce a pedagogical method used in a design studio as part of a curriculum-greening process to encourage reflection on the complexity of sustainability and sustainable design. Online reflective journals were used in two semesters of a sustainable design studio to develop students' awareness and understanding of concepts relating to sustainability and sustainable design. Design/methodology/approach: In the first seven weeks of a semester-long senior design studio, interior design students recorded their reflections on readings and in-class discussions on sustainable thinking, sustainable actions and sustainable design. The content analysis of the journal entries (n = 226) of two such groups of students (n = 30) from two different semesters are presented in this paper. In assessing the pedagogical effectiveness of the technique in the design studio, Hatton and Smith's framework on the four operational aspects of reflection--descriptive, descriptive reflection, dialogic reflection, and critical reflection--is used to discuss the levels of reflection in the journal entries. Findings: All four levels of reflection are represented in the journal entries analyzed for this paper. Results indicate that depth and complexity of thought are possible to achieve within a semester long course and can be used as a starting point for design development using complex concepts such as sustainability. Originality/value: The pedagogical effectiveness of reflective journal writing in a sustainable design studio is assessed. By adding a reflective writing component to a design studio format that otherwise primarily engages students' visual and verbal skills, the paper offers one approach to greening the design curriculum. (Contains 1 table.)