This research aims to use Pilates exercises (outside and inside) in the water for juniors under 13 years old and to identify its impact and on some physical abilities and the level of performance of starting and rotation in swimming crawling on the abdomen, by identifying: 1- The effect of Pilates training on improving some of the physical abilities of swimming juniors under 13 years old 2- Identifying the differences between the two research groups (experimental and control) in some physical abilities represented in (muscular strength, endurance, speed, strength characterized by speed, muscular ability, flexibility, compatibility, balance). 3- Identifying the differences between the two research groups (experimental and control) in the level of performance of starting and rotation of the abdominal crawling swimming. The researcher used the experimental method with a pre- and post-measurement for two groups, one of them is experimental and the other is control, due to its suitability to the nature of this research. Second: a community and a sample of the research: The research community included male swimming juniors in Marseille Club in Mit Ghamr and registered in the Workers Club of Zagazig University, for the age group 11-13 years (born in 2008-2009-2010 CE), and their number was (28) juniors during the sports season 2020/2021 In light of the objective and hypotheses of the research and within the limits of the research sample and its characteristics, and according to what was indicated by the results of the statistical analysis, the researcher was able to conclude the following: 1- Pilates exercises (outside - inside) the water improve some physical abilities (muscular strength - endurance strength - muscular ability - strength characteristic of speed - speed - compatibility - flexibility - balance) for swimming juniors under 13 years old. 2- Performing Pilates exercises (outside - inside) the water contributed to improving the level of starting and spinning performance in belly crawl swimming for junior swimmers under 13 years old. 3- The results of the study showed that the experimental group was better than the control group, which used the traditional program 4- Regular training led to an increase in physical efficiency and level of performance 5- The method used in training the control group by repeating the performance contributed to the development of some physical abilities and raising the level of performance, but a lower percentage than the experimental group.