The present study aimed to evaluate the use of metaphors by preservice science teachers on the subject of genetically modified organisms (GMOs). In the study, a phenomenology method was employed in the scope of a qualitative research model. The study group was composed of 189 preservice teachers who were employed in various science fields (e.g., biology, physics, chemistry, science) at a state university during the spring semester of the 2016 to 2017 academic year. In the form used for data collection, the preservice teachers were asked to fill in the following query: 'GMO is like ……… because ………'. The data collected in this scope were analysed with frequency (f) and percentage (%) calculations and the results derived from these analyses were listed in tables. It was determined that, among the 189 preservice teachers, 150 valid metaphors were generated, while 39 were invalid. The metaphors gathered with the query posed in the first section of the data collection process were grouped into six categories according to their similarities and common characteristics, as follows: Causing changes in appearance or structure; having harmful effects; having beneficial effects; having harmful effects though seemingly beneficial ones at first glance; having both beneficial and harmful effects; and having harmful effects that occur over time. The largest number of metaphors was found in the 'causing changes in appearance or structure' category, with a value of f = 51, while the smallest number of metaphors was found in the 'having beneficial effects' category, with a value of f = 6. From this study, it was determined that a large number of preservice teachers have negative perceptions as well as some misconceptions of the concept of GMOs.