The aim of this study was to determine the effects of 8-week thera-band training on swimming performance of 11-13-year-old age group female swimmers. Twenty-one volunteer female athletes who regularly swim in the Gebze Denizyıldızları Swimming Club participated in the study and the swimmers were randomly divided into three groups: Experimental-1, Experimental-2 and Control groups. Experimental-1 (n = 7; average age = 11.85 ± 0.89 years; average weight = 47.02 ± 7.45 kg; average height = 148.00 ± 0.84 cm) had resistance band in water + swimming training, Experimental-2 (n = 7; average age = 12.00) ± 0.81 years; average weight = 51.67 ± 7.16 kg; average height = 152.29 ± 0.50 cm) had resistance band on land + swimming training and Control group (n = 7; average age = 11.85 ± 0.89 years; average weight = 52.08 ± 1.00 kg) average height = 153.43 ± 0.47 cm) had only club swimming training. Before and after 8-week training program, test values of swimmers in terms of 30 seconds sit-up, 30 seconds push-up, 30 seconds medicine ball toss, standing long jump tests, and 25-50-200m swimming degrees were measured. Thera-band exercises in water and land were applied to athletes three days a week before swimming training. SPSS 22.0 package program included descriptive statistics, Wilcoxon test was used for intra-group analysis and Mann Whitney U test was used for intergroup analysis, and significance level was calculated as p<0.05. As a result of the study, no improvement was observed between the resistance training of the swimmers in the water and on the land, but it was observed that there were significant improvements in the degrees of swimming and sit-ups, push-ups, standing long jump and medicine ball toss test measurements in comparison of both water and land resistance training with the control group (p<0.05). From this point of view, it can be said that thera-band resistance trainings applied on both water and land three days a week for 8 weeks have a positive effect on the swimming performance of 11-13-year-old age group swimmers.