This research has been made to define the acute effects of static streching on vertical jump performance in children. The research has been applied on 49 healthy male volunteer athletes who have been taking basketball education for 2.1±0.2 years.(age:12.6±0.7 years, height: 157.9±6.9 cm, weight: 49.7±6.7 kg) Two different protocols have been made in this research. In the first protocol, 5 minutes aerobic density and 5 x 10 m forward, backward, side general warming up exercice in submaximal level has been applied on each child and in the second protocol, after general warming up, static streching practice has been applied to the same children. After each warming up and streching practice, countermovement jump performance have been measured. Active static streching practice has been applied in a strech sensitivity for 3 times 30 seconds and 15 seconds brakes between repetitions. Descriptive statistical methods and Paired-Samples T test have been applied on statistical analysis of vertical jump data that belong to children. Children jump 28.6 ± 1.1 cm. after a general warming up without any streching practice whereas the children who have made static streching application after warming up jump 27.1 ± 1.3 cm. The1.5 cm. difference (%5.2) has been found significant (t = -10.476; p<0.001). As a result, static streching practice after general warming up effects vertical jump performance negatively.