This study empirically compared differences between the expository writing performance and writing motivation of secondary student writers according to whether they selected a topic. In total, 196 middle school students from Seoul participated in this study, which analyzed the associations of the student’s topic-presented and topic-selective expository writing in two sessions with their motivation. This study found the following. First, a paired sample t-test showed that secondary students had higher writing fluency(number of letters, words, sentences) and took longer when performing topic-selective writing than topic-presented writing. Second, the paired sample t-test, showed that secondary students achieved better writing quality(only content and expression were significant). Third, paired sample t-test, found that secondary students had higher motivation(just in writing attitude and writing efficacy were significant) for topic-selective writing. Fourth, one-way ANOVA of writing motivation according to the group by writing level found that the sensitivity to the type of topic presentation increased in the order upper > lower > middle group levels.