The purpose of this study was to investigate the pathologic changes of jumper's knee before and after jumping and effects of icing after jumping. Sixteen healthy college students and sixteen collegiate volleyball players with jumper's knee were divided into two groups by eight, without icing group and with icing group after jumping exercise. Without icing groups rested for 20 minutes, while with icing groups were treated with ice for 20 minutes after eighty times of jumping. Signal to noise ratio (SNR) and sectional area of patellar tendon with Magnetic Resonance Imaging and the tenderness of patellar tendon with visual analog scale were measured before and after exercise, following with or without icing and 24 and 48 hours later from the treatment. In jumper's knee group, significant increase was found in the SNR, sectional area of patellar tendon, and tenderness of patellar tendon after exercise compared to before exercise. In addition, in jumper's knee with icing group, significant decrease was found in the SNR, sectional area of patellar tendon after icing and 24 and 48 hours after icing, and the tenderness of patellar tendon after icing compared to after exercise. These results suggested that icing was an effective treatment for jumper's knee after exercise.