Objective To compare surgical outcomes of Stanford type A acute aortic dissection between operations at midnight and daytime. Methods From January 2004 to March 2013，195 patients with Stanford type A acute aortic dissection received surgical treatment in Nanjing Hospital Affiliated to Nanjing Medical University （Nanjing Cardiovascular Disease Hospital）. Patients with identical or similar propensity scores were matched from 127 patients who underwent emergency operation at daytime and 68 patients who underwent emergency operation at midnight. A total of 58 pairs of matched patients which had the same or similar propensity score were selected in daytime surgery group （n=58，43 males and 15 females，47.7±14.6 years） and midnight surgery group （n=58，45 males and 13 females，48.3±14.6 years）. Operation time，postoperative chest drainage，mechanical ventilation time，postoperative incidence of dialysis and tracheostomy，length of ICU stay and in-hospital mortality were compared between the daytime group and midnight group. Results A total of 58 pair of patients were matched in this study. There was no statistical difference in postoperative incidence of tracheostomy ［19.0% （11/58） vs. 6.9% （4/58），P=0.053］ or in-hospital mortality ［8.6% （5/58） vs. 6.9%（4/58），P=0.729］ between the midnight group and daytime group. Operation time （485.7±93.5 minutes vs. 428.5±123.3 minutes，P=0.048），postoperative chest drainage （979.5±235.7 ml vs. 756.6±185.9 ml，P=0.031），mechanical ventilation time （67.9±13.8 hours vs. 55.7±11.9 hours，P=0.025），postoperative incidence of dialysis ［17.2% （10/58） vs. 5.2%（3/58），P=0.039］ and length of ICU stay （89.4±16.2 hours vs. 74.8±12.5 hours，P=0.023） of the midnight group weresignificantly longer or higher than those of the daytime group. A total of 107 patients were followed up for 4-6 months after discharge. During follow-up，there was no late death. Among the 13 patients who required postoperative dialysis，12 patientsno longer needed regular dialysis. Conclusion Emergency operation at midnight does not increase in-hospital mortalitybut increase some postoperative morbidity in patients with Stanford type A acute aortic dissection. Whether at midnight or daytime，better preoperative preparation and surgeons’ vigor are needed for timely surgical treatment for patients with Stanford type A acute aortic dissection.