Purpose: The aims of this study were to assess the clinical characteristics of patients with postoperative myasthenic crisis (PMC) and to identify the risk factors affecting the occurrence of PMC. Method: Extended thymectomy was performed on 178 patients with generalized MG with a mean onset age of 36.8 years. The potentially risk factors were analyzed by binary logistic regression analysis. Result: During the over five-year follow-up, 44 patients (24.7%) experienced 58 episodes of PMC. The mean interval between surgery and the first episodes of PMC was 13.8 months, and for 81.8% of the patients it occurred within the first 2 years after thymectomy. Nine of 16 patients (56.3%) with a history of preoperative MC had recurrent crises. Respiratory tract infection was the most common precipitant of PMC. Univariate analysis showed that age at onset, preoperative MGFA class, preoperative MC, presence of bulbar symptoms, operation duration, amount of intraoperative blood loss, and the presence of thymoma were significantly associated with the occurrence of PMC. However, multivariate logistic regression analysis revealed that a history of preoperative MC (OR = 2.845, p = 0.044), presence of bulbar symptoms (OR = 3.062, p = 0.027), and longer operation duration (OR = 1.026, p = 0.009) were the independent risk factors for PMC. Conclusion: The important risk factors for developing PMC in generalized MG patients include the presence of bulbar symptoms, history of preoperative MC, and longer operation duration. Optimization of the preoperative evaluation and proper perioperative care of MG patients may decrease the frequency of PMC.