The current study aims to determine science student teachers' cognitive structure on the concept of food pyramid. Qualitative research method was applied in this study. Fallacies detected in the pre-service teachers' conceptual structures are believed to result in students' developing misconceptions in their future classes and will adversely affect their future teaching performance. The data were collected from 48 science student teachers. A free word association test was used as a data collection instrument. The data collected were subject to content analysis. Analyzing the science student teachers' responses to the concept of food pyramid on the free word association test, these responses were coded and divided into categories. Based on the categories, frequency and percentages were provided. The data collected through the study were divided into 7 categories, which were stated as follows: -relationship between producer, consumer and decomposer in matter and energy flow-concepts related to nourishment pyramid-definition of food pyramid-energy and matter transfer-producer, consumer and decomposer-elements of ecosystem and ecological factors-scientific disciplines related to food pyramid. When the words provided as answers by the science student teachers to the concept of food pyramid were analyzed, it was noticed that they had more word connections with relationship between producer, consumer and decomposer in matter and energy flow. It can be argued that some students could not produce any sentences and some others could not make meaningful sentences. Moreover, it was determined that they had some misconceptions about food pyramid. Similar research can be conducted with different student groups and for the correction of alternative concepts related to the concept of food pyramid, extra biology courses should be included in undergraduate curriculums.