The purpose of this research was to determine the effects of the swimming training program on stress levels of the students ages 11-13. To this end, 60 students from Private Sahin School in the Sakarya city participated in the study voluntarily. 60 students were divided into two groups and each group was included 30 students. Stress Level Scale II developed by Leighton (1989) was used in the study for pretests and posttests. After preliminary testing, the experimental group students participated in the swimming training in two sessions, each lasting two hours for 8 weeks. Posttests for two groups were administered at the end of the swimming training program. The data obtained from the present study conducted with an experimental design method were analyzed using SPSS statistical software. T test was used in the study to compare the results between pre-posttests of the experimental group and pre-posttests of the control group in different groups (Pretest of the experimental group x Pretest of the control group/Posttest of the experimental group x Posttest of the control group). Also, paired Sample T test was used in the study to compare the results between pre-posttests of the experimental group and pre-posttests of the control group in the same groups (Pretest of the experimental group x Posttest of the experimental group / Pretest of the control group x Posttest of the control group). As a result of this study, there was a significant difference between pretest of the experimental group (39.03 ± 9.21) and posttest of the experimental group (31.20 ± 4.06). There was not a significant difference between pretest of the control group (36.43 ± 8.13) and posttest of the control group (40.56 ± 9.21). Research results showed that swimming training program was effective to reduce stress level of the students ages 11-13.