For reading-integrated writing tasks, L2 writers` inappropriate source use has been a continuous issue. Thus, this study is designed to investigate Korean college students` textual borrowing behaviors in summary writing, a reading-based writing task. Textual borrowing was assessed in terms of individual words and word strings based on text difficulty (easy vs. difficult) and text structure (comparison vs. description). To examine borrowing of individual words, the RANGE program was used, which provides the percentage of the shared vocabulary between texts in terms of token, type, and family. As for borrowing of word strings, three variables were adopted: exact copy, near copy, and paraphrase. An analysis of 228 summary protocols showed that text difficulty had a significant influence on borrowing of individual words, but not word strings. Also, it was found that text structure did not have a direct impact on borrowing of both individual words and word strings, except for paraphrasing. The findings indicate that L2 writers` source text dependency is strongly related to text difficulty rather than text structure. Based on the results, pedagogical implications were suggested.