The current study aims to determine biology student teachers' cognitive structure on the concept of "living thing" through revealing their conceptual framework. Qualitative research method was applied in this study. The data were collected from 44 biology student teachers. A free word association test was used as a data collection instrument. The data collected were subject to content analysis. Analyzing the biology student teachers' responses to the concept of living thing on the free word association test, these responses were coded and divided into categories. Based on the categories, frequency and percentages were provided. The internal validity of the themes and subthemes categories was ensured by the author and two experts in Biology. The data collected through the study were divided into 7 categories. These categories were: examples of types of living things based on the levels of classification, levels of organization, characteristics of living things and metabolism, cell and its organelle, energy in living things, environment occupied by living things and the reactions shown to the conditions of the environment, and the concepts that a living thing revokes. When the words provided as answers by the biology student teachers were analyzed, it was noticed that they had closer word connections with the category of "examples of types of living thinks based on the levels of classification" than "characteristics of living thinks and metabolism" and "energy in living things". Moreover, it was determined that they had some misconceptions about living thing.