In this study, we determined cognitive structures and misconceptions about basic ecological concepts by using "word association" tests on secondary school students, age between 12-14 years. Eighty-nine students participated in this study. Before WAT was generated, basic ecological concepts that take place in the secondary science curriculum were determined. And then these concepts; "Environment", "species", "habitat", "population", "ecosystem", "food chain", "substance cycle", "biological diversity", "environmental pollution", "global warming", "acid rain" and "greenhouse effect" were determined as keywords. Also, students were asked to construct a related example sentence for each keyword. Analysis of data was done in four steps: Determination of the responses given for the keywords, calculation of the Relatedness Coefficient between the keywords, formation of concept web that put forward the relation for the given responses to keywords, and analysis of constructed sentences for each keyword. In conclusion, this study put forward that most of the students had weak cognitive structure about ecological concepts. The close relations among these concepts with each other could not be built in students' cognitive structure. Most of the students' responses were superficial knowledge acquired in daily life and contained many misconceptions. Although students were aware of environmental problems, they were deficient in scientific information about reasons and effects of these problems. This case shows that we are not sufficient in environmental education and training.