By using the questionnaire survey and the investigation results of using the questionnaire-Elementary School Students' After School Sport Participation Motivation. The purposes of this study were to compare the differences of elementary school students' after school sport participation motivation. Then, according to the conclusion of this study, some suggestions were offered. The samples of this study were the fifth and sixth grade students in Kaohsiung city elementary school. The variables were gender, grade, and socioeconomic status. The statistical methods used in this study were t-test, one-way ANOVA, and descriptive statistics. The results of this study were the followings: To compare after school sport participation motivation of different gender, grade, and socioeconomic status students in elementary school: 1. The fifth and sixth grade students were significantly different in "Knowledge Pursuing" factor. 2. The boy and girl were significantly different in such factors as "Knowledge Pursuing" and "Health and Fitness". 3. The low socioeconomic status and high socioeconomic status students were significantly different in "Health and Fitness" factor. 4. The low socioeconomic status and middle socioeconomic status students were significantly different in "Score" factor. And between low socioeconomic status and high socioeconomic status students were, too. 5. The low socioeconomic status and high socioeconomic status students were significantly different in the total score. Finally, the comprehensive analysis and discussion were provided that based on the results of this study. Then, some suggestions were offered for educational administration units, schools and further studies to reference.