The purpose of this study was to examine the effect of playing mini-games of soccer for improvement of physical fitness. The subjects were 21 students at I junior high school (I Group) and 22 students at S junior high school (S Group). Group I played a mini-game with changed rules, whereas group S played the full game, each over a period of three weeks (6 physical education classes). Before and after the classes, skill tests (passing and dribbling), fitness tests (150m sprint with changing direction ; 25m×6 times, rest interval 30s), and a test game were conducted. In addition, an after-class questionnaire on knowledge, how to learn and skill of soccer was conducted. The main results were as follows : 1) The results of the passing and dribbling tests were improved significantly after classes using the mini-game. There was no significant improvement in the results of the first set of 150-m sprints with a change in direction after classes in both group, whereas the mean time for 6 sprints was improved significantly after classes in both groups. 2) There were no significant differences in the number of ball touches, heart rate or RPE in test games after classes in both groups, whereas the total movement distance was decreased significantly after classes using the full game. 3) In the questionnaire after the test game, almost every item on technique (coordination), physical fitness and mentality tended to have a higher score after classes using the mini game. On the other hand, after classes using the full game each mentality-related item tended to have a higher score, whereas items related to technique (coordination) and physical fitness tended to score the same or lower. 4) In the questionnaire after the class, there was no wide difference in knowledge of soccer between both groups, whereas items related to how to learn and skill of soccer tended to score higher in the former than in the latter. These results suggest that improvement of energy-related physical fitness could be obtained without compromising students' interest, volition and attitude regardless of whether they played the mini-game or the full game, although use of the mini-game led to an effective improvement of technique (coordination) without decreasing students' consciousness of how to learn soccer skills.