Although osteochondral grafting surgery is believed to replace damaged cartilage with healthy-looking normal cartilage, no study focuses on ultrasound quantification of those cartilage immediately after the surgery. It is unknown whether the ultrasound properties of damaged cartilage from trauma or osteonecrosis are same with each other. We have examined ultrasound properties of damaged cartilage, adjacent intact cartilage and plug cartilage during osteochondral grafting surgery for 15 knees of 15 patients, mean age of 43.4 (range, 14-61) years. Results showed that signal intensities of ultrasound (a measure of superficial cartilage integrity) of intact cartilage, damaged cartilage, and plug cartilage were 1.91 (arbitrary unit), 0.40, and 2.13, respectively, in 11 knees of 11 patients of traumatic cartilage lesions. Interval between signals of ultrasound (a parameter related to thickness) were 2.79 (mu s), 1.90, and 2.85, respectively. The signal intensity and the interval between signals of plug cartilage were 533% (P < 0.01) and 150% (P < 0.01) of damaged cartilage, respectively. In four knees of four patients of osteonecrosis, the signal intensities of intact cartilage, damaged cartilage, and plug cartilage were 1.25, 0.30, and 1.39, respectively. The interval between signals were 2.36, 2.00, and 2.69, respectively. The signal intensity and the interval between signals of plug cartilage were 463% (P < 0.01) and 135% (P < 0.05) of damaged cartilage. We conclude that ultrasound properties of the damaged cartilage from trauma or osteonecrosis did not differ a lot especially in the late stages of osteonecrosis and that the osteochondral grafting surgery replaced the damaged cartilage with plug cartilage that had greater superficial cartilage integrity and greater thickness parameter immediately after the surgery. Long-term effect of the osteochondral grafting surgery should be verified in further study.