Background and objectives Breast cancer is one of the most common malignant tumors in women. Herein, we compared the analgesic efficacy of ultrasound-guided rhomboid intercostal nerve block , erector spinae plane block and serratus plane block after modified radical mastectomy of unilateral breast cancer. Methods: A total of 90 patients who underwent modified radical mastectomy for unilateral breast cancer were selected. patients were randomly allocated into three groups receiving ultrasound-guided serratus plane block, erector spinae plane block, and the rhomboid intercostal block group. All groups received 20 mL 0.5% ropivacaine. Within 24 hours after operation, the patient received intravenous injection of tramadol 1-2 mg/kg to relieve pain in the surgical ward. Results: The dosage of tramadol 24-hours postoperatively in the rhomboid intercostal block and erector spinae plane block groups was significantly lower than that in serratus plane block group (P < 0.001). There was no statistical difference in tramadol consumption between the erector spinae plane block and rhomboid intercostal block groups within 24 hours (P = 0.676). The numerical rating scale scores in the erector spinae plane block and rhomboid intercostal block groups at 0.5, 1, 3, 6, 12, 18, and 24 hours postoperatively once patients were active were significantly lower than in the serratus plane block group (P < 0.05 for all comparisons); however, The numerical rating scale scores between rhomboid intercostal block and erector spinae plane block groups did not differ significatively within 24 hours after surgery when patients were active. Conclusions: Ultrasound-guided rhomboid intercostal block and erector spinae plane block can reduce the dosage of tramadol and NRS score compared with serratus plane block after modified radical mastectomy.