The purpose of this study was to investigate the ways student writers use source texts for their own composition. In this study, 60 high school students read 5 source texts and wrote a text using informations in those source texts. This study found out that 10th grade students tended to focus on source texts which contain informations being strongly related to the writing task`s topic. The results of participants` evaluation of 5 whole source texts` usefulness, however, was not unanimous. Some students` reason to evaluate source texts was based on the existence of useful informations; on the other hand, some students focused on their own reading ability, personal interest or learning. Also, participants tended to evaluate the result of their information selecting practice negatively rather than positively and felt that they struggled to read source texts and to select informations. This indicates that many students did not have sufficient experience to use source texts to write information texts. Educators need to find out ways to help student writers use source texts and select information proficiently.