BACKGROUND Active bleeding due to arterial injury following the acupuncture can sometimes represent a life-threatening complication. Only few reports of an actively bleeding hematoma diagnosed by contrast-enhanced ultrasound, which enables the depiction of vascular, have been reported. CASE SUMMARY Here, we report the case of a 75-year-old woman, who presented with sudden swelling, ecchymosis, and pain in the upper left limb. She underwent an acupuncture treatment of traditional Chinese medicine followed by a deep shoulder massage 2 d before admission to hospital. A few hours after the massage, her left upper arm was red, swollen and progressively aggravated. Ultrasonography showed a large hematoma (11.2 cm x 3.5 cm x 3.4 cm) beside the left brachial artery. Color Doppler ultrasound revealed that blood flow signals of the arteries branched into the hematoma. The contrast-enhanced ultrasound showed microbubbles from the brachial artery passing into the hematoma, diffused within the hematoma with the local surge of red blood cells, and disappearing after approximately 17 s. The microbubbles were likely due to bleeding from the arteries. After pressure bandaging treatment, the hematoma became smaller (3.1 cm x 1.7 cm) and organized according to ultrasonography performed 20 d later. CONCLUSION This case highlights the ultimate importance of contrast-enhanced ultrasound for the diagnosis of an actively bleeding hematoma.