Abstarct: Respiratory function status in swimmers plays a key role in their performance. Some muscles involved in core stability and pulmonary function are same and the role of the two variables is considerable in swimmers performance. Hence, the purpose of present study was investigating the relationship between core stability and pulmonary function in trained swimmers. In order to achieve the purpose of the study, 40 girl swimmers between the age group of seven to fifteen years were purposefully selected as research samples. Subjects were divided into two groups according to their history of regularly swimming exercise, 29 subjects (Group 1) - Duration of swimming more than three years, 11 subjects (Group 2) - Duration of swimming less than one year. Measurement of pulmonary variables was taken with a digital spirometer in the setting position. The McGill protocol was used to measure the core stability. Analyzing the data by Pearson's correlation test showed that there are not significant relationships between core stability tests and static and dynamic pulmonary function in two groups. The Pearson's correlations in group II were higher compare to group I. The multiple regression analysis included all independent variables and identified Right Side Plank test in group I and Left Side Plank and Back Extension tests in group II as significant predictors of pulmonary function. This may be concluded from this study that there are not the significant relationships between core stability and pulmonary functions in trained swimmers and regular prolonged swim training decreases the relationships in swimmers. Therefore, we need to do some more researches for identifying the other factors that affect the relationship between core stability and pulmonary function that help to sport performance enhancement in trained adolescent swimmers.