In this study, it was aimed to investigate the cognitive structures of classroom teacher candidates on some basic science concepts. Word association test (WAT) technique was used to gather data. Twelve keywords related to basic physics, chemistry, and biology concepts were determined and used in the formation of WAT’s. Forty-three classroom teacher candidates studying at 2nd classes at an education faculty were the participants of this study. Data obtained by WAT were examined by using number of different responses given to each keyword, and by drawing concept maps according to both frequencies and relatedness coefficients. A cut-off point technique was used when drawing the concept maps. Because of this study, it can be said that participants have moderate cognitive structures on the investigated science concepts and their cognitive structure was strongest on chemistry concepts and weakest on biology concepts. Article visualizations