Architects and planners should design pleasant and healthy places to enhance public well-being. Sustainable planning can achieve that goal. Yet, studies showed architects and planners failed to plan for sustainable development. The lack of knowledge about sustainability among planning students (future planning practitioners) may caused that end. However, no study has tested the level of sustainability knowledge among planning students. This study investigated the knowledge of planning students about seven dimensions of sustainability (legal aspects, research areas, existing pre-judgements, sustainability principles in general, sustainability principles about planning aspects, sustainability principles about architectural aspects). Whether the planning students perceive designing sustainable environments as their own responsibility and what sources of information (lectures, seminars, studio classes, academic literature, magazines and visual media) they use to promote their knowledge of sustainability was also explored. 80 volunteers (from first year to fourth year) studying in the Department of City and Regional Planning at Dokuz Eylul University and 20 people who has no planning background participated in the study. Data were collected mainly by means of questionnaires. Comparisons between planning students and lay-people showed that lay-people, who has no planning education, are as knowledgeable as planning students about seven dimensions of sustainability. Comparisons between planning students in different educational levels showed that sustainability knowledge does not increase as educational stages increase. Although students reported designing sustainable plans is their own responsibility, they usually rely on magazines and visual media to promote their knowledge of sustainability rather than lectures, seminars, and studio classes. This study is important in highlighting the problem of this deficient knowledge among planning students and in listing some recommendations for planning education to improve sustainability literacy among planning students. The sample of participants in this study was derived from city and regional planning department of one university. Whether the results of the present study will apply to different schools in Turkey remains to be seen, and more work needs to be done to test the generalization of the results to various cultures as well.