This study aimed to examine 6 th graders' cognitive structures in regards to renewable energy. This research was designed with cross-sectional survey model. Word association test on renewable energy was used as a data collection tool for 366 6 th graders in Mersin. The concepts of "renewable energy, solar energy, hydroelectric energy, geothermal energy, biomass energy and wind energy" were selected from the curriculum and used as keywords in the word association test. When the associations made by keywords were examined quantitatively, it was found that students made more associations with sun and wind concepts. It can be argued that fewer associations were made with keywords such as hydroelectric, geothermal and biomass. Both the quantity and the quality of the relationships between the keywords were revealed in the process of creating the concept network. The results showed that students had difficulty in associating the key concepts of "biomass" and "hydroelectricity" with renewable energy. In addition, it was concluded that students had a low level of knowledge about the concept of "biomass energy" and that the concept could not be associated with other concepts. This result is thought to be related to the insufficient number of acquisitions and class hours in the science education curriculum. In this context it is recommended to increase the number of acquisitions and the time allocated to for these acquisitions so that student knowledge about renewable energy sources can be improved.