Objective To investigate the effects of photobiomodulation on the stellate ganglion region in patients undergoing breast cancer surgery， specifically on their postoperative sleep disturbance and pain. Methods A total of 114 patients who were scheduled to undergo modified radical mastectomy for breast cancer under general anesthesia at Baoding First Central Hospital from June 2024 to December 2024 were selected. The participants were aged between 18 and 65 years， with an ASA physical status of Ⅰ - Ⅲ and a body-mass index ranging from 18 - 30 kg/m2. By using a random number table， the patients were randomly allocated into either the control group （Group C） or the intervention group （Group T）. Patients in Group C did not receive any intervention， whereas those in Group T underwent linearly polarized light irradiation over the stellate ganglion region after general anesthesia. The irradiation parameters were set as follows： A power setting of 80%， an irradiation/intermittent cycle of 2 seconds/4 seconds， and a total duration of 40 minutes. Data were recorded for both groups on the day before surgery （D0）， postoperative day 2 （D2）， and postoperative day 5 （D5）， including the Pittsburgh Sleep Quality Index （PSQI） score， total sleep time （TST）， sleep efficiency （SE）， and the number of nocturnal awakenings （NA）. Additionally， the Visual Analog Scale （VAS） scores on D2， the number of effective patient-controlled analgesia （PCA） presses within 48 hours after surgery， the incidence of postoperative adverse events， and patient satisfaction were compared between the two groups. Results Patients in the T group showed significantly lower PSQI scores and a lower incidence of post-operative sleep disorder （PSD） on the D2 and D5 compared to those in Group C （P < 0.001）. In comparison with Group C， the T group had significantly longer TST and higher SE on D2 and D5 （P < 0.001）， as well as a significantly reduced NA （P < 0.001）. When compared to Group C， the T group presented a significantly lower VAS score and a notable reduction in the total number of PCA compressions on D2 （all P < 0.001）. Moreover， the incidence of nausea and vomiting was significantly lower in the T group than in Group C （P < 0.001）， whereas patient satisfaction scores were significantly higher （P < 0.001）. Conclusion Photobiomodulation applied to the stellate ganglion region can reduce the incidence of PSD， improve sleep quality， alleviate pain， and enhance patient satisfaction in breast cancer patients， while maintaining a favorable safety profile.