The purpose of the study was for investigating the effect of therapeutic ultrasound irradiation on HSP70 expression in knee of degraded rat articular cartilage. Knee of ten Sprague-Dawley male rats were immobilized for 4 weeks and divided at random into the control and continuous ultrasound applicated group. The continuous ultrasound applicated group was irradiated with frequency 1MHz, intensity $1W/cm^2$ for 5 minutes. The control group was sham sonication. The immunoreactivity of HSP70 was increased in degraded articular cartilage after untrasound irradiation. These results suggest that therapeutic ultrasound can enhance HSP70 expression in degraded articular cartilage.