The analysis of pre-service teachers' concept images can provide information about their mental schema of fractal dimension. There is limited research on students' understanding of fractal and fractal dimension. Therefore, this study aimed to investigate the pre-service teachers' understandings of fractal dimension based on concept image. The descriptive method was used in this study. The sample under investigation comprised of 78 (26 males and 52 females) freshmen pre-service elementary mathematics teachers at Afyon Kocatepe University in Turkey. Data was collected by an open-ended questionnaire and clinical interview. The questionnaire was developed by the researcher based on previous studies in the areas of teaching and learning fractals. Data was categorized by semantic content analysis and analyzed using descriptive methods. Analyzing the data gathered from clinical interviews, themes determined in the questionnaire were taken into consideration. The findings showed that pre-service teachers had difficulty in understanding fractal dimension and in making sense of it. Moreover, pre-service teachers could calculate fractal dimension, but they were not aware of what was being calculated completely.