Geometry is not only an essential tool to develop students' spatial thinking, but it is also a content strand that provides opportunities for them to develop ability to question, analytic thinking and reasoning skills. The current educational reforms emphasize that students should gain the ability to recognize geometric shapes and solids as well as to classify them hierarchically from early grade levels. In this study, the ability of pre-service mathematics teachers to recognize and classify geometric concepts (quadrilaterals and geometric solids) was investigated. For this purpose, a geometry questionnaire consisting of 10 open-ended questions was developed by the researcher based on an extent review of the existing literature. As a result of the preliminary examination of the pre-service teachers' responses to the questionnaire items, individual interviews were conducted with five pre-service teachers, who were thought to have different levels of thinking. The findings of the study showed that the vast majority of the pre-service teachers did not fully comprehend the hierarchical classification between quadrilaterals. In addition, this study demonstrated that pre-service teachers generally used prototype judgments to identify geometric solids and select examples and non-examples of geometric solids. Another finding of this study was that the pre-service teachers identified incorrect hierarchical classification between geometric solids. The findings of the study is discussed under the light of other studies in the literature and the recommendations of educational reforms.