This study was set up to determine the relationship between physical constitution and physical fitness on the one hand and swimming performance on the other. For this purpose, nine physical constitution tests, sixteen physical fitness tests and fifteen swimming performance tests were carried out using 4 6primary school male swimmers as subject. The main results can be summarized as follows: 1) There were significant correlations between swimming performance and abdominal girth, vital capacity, grip strength and reaction time. 2) There were distinct differences in back strength between first and second grade swimming performance groups.