Re‐tearing after arthroscopic rotator cuff repair (ARCR) frequently occurs, and high stiffness of the rotator cuff may be one of the factors. We investigated changes in stiffness of the supraspinatus muscle and tendon after ARCR as measured by shear wave elastography (SWE) with B‐mode ultrasound, and compared the supraspinatus muscle stiffness of patients with recurrent tears and patients with healed rotator cuffs. Sixty patients with supraspinatus tears requiring ARCR underwent serial SWE of their supraspinatus muscles and repaired tendons. SWE was performed before surgery (Pre‐Op) and at 1 week, 1 month, 2 months, 3 months, 4 months, 5 months, and 6 months after surgery. Additionally, the repaired rotator cuffs were evaluated using magnetic resonance imaging at 6 months after surgery to classify patients into a healed rotator cuff group and a recurrent tear group. Differences in SWE values between the groups were assessed at each time point. The SWE value of the repaired tendon at 1 week after ARCR was significantly greater than at 3 and 6 months. The SWE value for the supraspinatus muscle at 1 month after ARCR surgery in the healed group was lower than at Pre‐Op and 4, 5, and 6 months after surgery, and it was also lower than that at 1 month after surgery in the re‐tear group. There were no significant differences between time points in the SWE values of the supraspinatus muscle in the re‐tear group. The SWE value of the muscle in the re‐tear group was greater than in the healed group at 1 month after surgery (p < 0.05). Increased SWE values at 1 month after ARCR may predict recurrent rotator cuff tears after surgery rather than evaluating the tendon.