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The purpose of this reseach is to examine the effect of plyometric exercise performed in two different training frequencies in the competition season to the dominant and non –dominant concentric isokinetic leg strength values at two different angular speeds. Young male basketball players of a sports club -average age is 15,77 ± 0.87- were taken to the training. 18 sportsmen were neutrally and equally (n=6) divided into three groups, two for the experiment and one group for the control. One of the experiment groups one day a week and the other three days a week practiced the drop jump plyometric exercise following the routine basketball training and then completed the training with stretching exercise. The control group ,on the other hand, completed the training with stretching exercise after routine basketball training. The training continued for eight weeks. The measurements were taken before and after eight-week-exercise. All the participant sportsmen were measured with a normcomputerized isokinetic dynamometer. (Cybex International, Inc. Ronkonkoma, NewYork, USA). Peak torque parameter was used as a muscular strength feature. In the research, statistical comparisons among three groups were calculated according to KruskalWallis test technique by measuring average values of the dependent variables and for the significant level of the differences Mann-Whitney U test and Wilcoxon Paired Samples test were used. significant level were determined as p<0,05. In the end of the trainings, the plyometric exercise groups’ peak torque values of concentric isokinetic knee extension and knee flexion at both angular speeds statistically showed significant progress (p<0,05). Compared to control group and one day a week plyometric exercise group, a significant increase was determined in the peak torque values of concentric isokinetic knee extension and knee flexion of three days a week plyometric exercise group (p<0,05). Whereas the peak torque values of concentric isokinetic knee extension and knee flexion was increasing in the groups that did plyometric exercise for eight weeks, no change was determined in the control group. Besides, the determined increase in the three days a week plyometric exercise group is significantly more than one day a week plyometric exercise.group.