The purpose of this study is to determine biology student teachers' cognitive structure with regard to "Blood". Qualitative research method has been used. The free word association test and the draw-write technique have been used in collection of data. The data obtained have been evaluated and divided into categories based on content analysis. According to the analysis results, in biology student teachers' conceptual structures with regard to blood, while nine categories have been determined for the free word association test, eight categories have been determined for the draw-write technique. Rich data supporting, dilating and explaining one another have been obtained through both measuring tools. In this context, it has been determined through two measuring tools that student teachers' cognitive structures are concentrated in the "blood cells" and blood "groups and determination of blood groups" categories. Furthermore, in the data collected through both measuring tools in the determined categories. It has been determined that student teachers have alternative concepts on blood concept.