Patients in critical care settings often require prolonged mechanical ventilation (MV) therapy and, occasionally, they cannot be weaned from MV. The authors evaluated the efficacy of acupuncture treatment for improving the respiratory status and promoting successful weaning from prolonged MV in patients at intensive care units (ICUs). Retrospective observational study. Gifu University Hospital, Gifu, Japan. The authors included 16 tracheostomized patients receiving MV for >21 days at the ICU of Gifu University Hospital, who underwent acupuncture therapy for improving their respiratory status. Acupuncture treatment was conducted in four sessions per week. The data of tidal volume (VT), respiratory rate (RR), heart rate (HR), oxygen saturation as measured by pulse oximetry (SpO2), dynamic lung compliance (Cdyn), rapid shallow breath index (RSBI; RR/VT) values before and immediately after acupuncture were extracted from the medical records. The median number of days on MV before acupuncture initiation was 31 days. VT and Cdyn were significantly increased immediately after acupuncture (all p < 0.001), whereas RR, HR, and RSBI were significantly decreased (all p < 0.05). Eleven patients were successfully weaned from MV after acupuncture initiation. In the weaning success group, VT and Cdyn were significantly increased (all p < 0.01), whereas RR, HR, and RSBI were significantly decreased (all p < 0.05) after acupuncture. Conversely, in the weaning failure group, these values were not changed significantly. The increase in Cdyn after acupuncture was larger in the weaning success group than in the weaning failure group (p < 0.05). Acupuncture treatment might have beneficial effects on the respiratory status of ICU patients receiving MV and may help in weaning from prolonged MV. Further large prospective cohort studies are warranted.