The research aims at the effect of simultaneous training on the endurance of the muscular capacity of the arms and the accuracy of the straight strike for the squash junior under 15 years old. The researcher used the experimental approach for the two groups, one experimental and the other a control one using the pre and post measurements for both groups. The research sample was chosen by the intentional method and included (17) juniors in a club Vanguards of the Army and registered in the Egyptian Squash Federation season 2018/2019 AD, and the training program lasted 6 weeks, with 3 training units per week, and the most important results of the research were that the simultaneous training for a period of 6 weeks led to the development of the muscular ability of the sponsors and the accuracy of the straight strike for the squash juniors under 15 years old.