This research was purposed to explore the relationship among sports involvement extents, sleep quality and fitness in elementary school children. The sports involvement extents of elementary school seniors, Pittsburgh Sleep Quality Index and school children’s health fitness were served as researching tools. The senior students of the elementary schools on the Xinwu Township of Taoyuan County were recruited to act as experimental subjects. Totally 500 questionnaires were delivered and 477 valid replies were received and rated at 95%. The data of questionnaire replies were further statistically analyzed by the Chinese Version SPSS18.0 to locate the correlation by means of Pearson Product-Moment Correlation and Multiple Stepwise Regression Analysis. Furthermore, the Multiple Hierarchical Regression Analysis was used to analyze the predictive explanatory power to fitness caused by sports involvement extents. Additionally, under the predictive situations with school children's sleep quality to serve as disturbance variables, the significance level was rated at α=.05. In view of research results, some facts were found and described as below. 1. In view of the dimensional relationship between the sports involvement extents and fitness among school children, the frequencies of sports involvement were lowly correlated to the fitness of standing long jump, sit-ups and cardio function; sports durations were lowly correlated to the fitness of standing long jump and sit-ups; sports intensity was lowly correlated to standing long jump, sit-ups and cardio function. Longer sports involvement durations ensured better fitness of standing long jump. Namely, students' stronger sports involvement and longer involvement durations wielded positive influence on the fitness of standing long jump. Higher frequencies of sports involvement ensured better performance in the fitness of sit-ups. Namely, school children's frequencies for sports involvement wielded positive influence on the fitness of standing long jump. 2. In view of the disturbance caused by sleep quality to sports involvement and fitness, the predictive power to the fitness of sit-ups caused by sports involvement extents reached a level of significance. It could be clearly seen stronger sports involvement extents ensured better performance in the fitness of sit-ups. In fitness, sit-ups were affected by the disturbance interactively caused by sports involvement extents and sleep quality.