The purpose of the study is to investigate pre-service elementary teachers' noticing expertise of students' mathematical thinking within the context of fractions. For this purpose, 32 pre-service elementary teachers were asked to examine students' answers and ways of thinking given in written excerpts related to fractions. The data was mainly analysed using the constant comparative method to identify similarities and differences in pre-service elementary teachers' answers based on the existing Professional Noticing of Children's Mathematical Thinking framework developed by Jacobs, Lamb, and Philipp ([2010]. Professional noticing of children's mathematical thinking. "Journal for Research in Mathematics Education, 41"(2), 169-202.). The findings indicated that the vast majority of the pre-service elementary teachers showed at least a limited level in all professional noticing skills: attending, interpreting, and deciding how to respond. The findings serve to inform teacher educators to include written excerpts in their mathematics teaching courses and, thus result in improvement in pre-service teachers' noticing skills.