This study aims to investigate the pre-service science teachers’ perceptions of protists. Within this scope, case study design was conducted. The data was collected from purposively chosen 60 third-grade pre-service science teachers from a university in Kayseri, Turkey during the spring semester of 2018–2019. The drawing-writing technique was used for data collection in the study. In the drawing test pre-service teachers were asked to choose three examples for the protists and draw them on the paper given. Moreover, they were asked to write the common features of the protists. The participants’ drawings and writings that reveal their conceptual structures regarding the protists were analyzed through content analysis method. The participants’ drawings and writings were analyzed based on the rubrics and grouped based on their levels. The percentages of the agreement between two experts regarding the assessment of drawings and writings were measured as 0.92 and 0.90, respectively, indicating a high reliability. In addition, Chi-square test was applied to the data in order to see whether there is a significant relationship between drawing and writing levels of the pre-service teachers. According to the findings, 11.7% of the participants had no/ irrelevant drawings and writings, 83.4% of them had partially correct drawings, and 5% of them had comprehensive drawings regarding protists. While only one participant wrote all six features for protists, 86.6% of them had partially correct writings including one to five features for protists. The findings revealed that pre-service teachers’ perceptions about the protists were identified as moderate, and there is a significant relationship between the pre-service teachers’ drawing and writing levels of protists. According to the (7x7) crosstabulation table, students with a high level of writing also have a high level of drawing and vice versa.