Core training has been widely used by trainers recently in order to improve the performance of soccer players. But the researcher doubts what effect it brings and how much coaches who work at Ethiopian soccer projects/programs are aware of its effect. The purpose of this study is to examine the effect of core strength training on physical fitness qualities on U-20 Tagel secondary preparatory school soccer trainees. To achieve the purpose, true experimental research design was used. The target population of this study were U-20 Tagel secondary preparatory school soccer trainees (N=24) were participated by using comprehensive sampling technique and randomly assigned into two equal groups. Among those, half of them were randomly selected as EG, to which specially prepared core strength training was applied, and the rest were CG. Age, height, and weight average values of EG and CG were similar, which are 17.75 years, 1.661 m, 55.67 kg, and 17.583 years, 1.653 m in height and 53.833 kg in weight, respectively. The experimental group (n = 12) performed core strength training three days per week for three months, and the control group (n = 12), however, did not perform this selected core strength training; both groups underwent a normal football training program. And both groups had taken pre- and post-tests. So, all subjects participated in five selected physical fitness tests: sit-up, sit-and-reach, Illinois agility test, 30 m dash run test, and explosive power (vertical jump). The data was analyzed and compared with the help of statistical procedures in which an arithmetic mean, standard deviation, and paired t-test were used. The level of p≤0.05 is considered a significant level. The result showed that on sit-up-test experimental group MD=- 13.75 & P=.000 while control group MD=-.66667 & P=.220, sit-and-reach test experimental group MD=-5.58333 & P=.000 & whereas control group MD=-.91667 & P=.102 and illinos agility test experimental group MD=.97250 & P=.000 while control MD=.08083 & P=.044, speed test experimental group MD=.40917 P=.000, while the control group MD=.00250 P=.960 & the explosive power (vertical jump) test experimental group MD=-.26083 P=.000 & while the control group MD=.00417 P=.546 As a result, the investigator recommended that adding core strength training to their soccer training program helps to improve trainees muscular endurance, flexibility, agility, speed, and explosive power.