Objective : The purpose of this study was to analyze ultrasonography and 90-90 SLR test on hamstring after both groups were applied static stretching exercise and PNF stretching exercise. Methods : For this experimental study, total 20 healthy university students, who were divided into static stretching exercise group and PNF stretching group. Each group was assessed before and after stretching(0.5 minute, 1 minute, 1.5 minutes, 2 minutes, 2.5 minutes, 3 minutes, 4 minutes, 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, 10 minutes). Results : Total score of 90-90 SLR test was showed a significant difference between pre and post. Hamstring diameter was gradually increased to 2.5 minutes and 3 minutes, where after it was gradually decreased in static stretching exercise group. Hamstring circumference had regular interval scores before and after on PNF stretching exercise group. Conclusion : There was a different change on hamstring diameter and circumference.