Background Thymectomy is considered the most effective treatment in patients with myasthenia gravis. This study aimed to explore the predictors of postoperative myasthenic crisis in patients with myasthenia gravis after thymectomy.Methods Clinical records of 243 patients with myasthenia gravis who underwent thymectomy were reviewed retrospectively. The following factors were analyzed in relation to the occurrence of myasthenic crisis after thymectomy:gender, age, duration of symptoms, Osserman stage, history of myasthenic crisis, concomitant diseases, preoperative pyridostigmine dose, preoperative steroid therapy, operation approach, operation time, presence of thymoma, major postoperative complications.Results Forty-four patients experienced postoperative myasthenic crisis during the first month after thymectomy.Univariate analysis revealed that Osserman stage (RR=0.0976, P=0.000), history of myasthenic crisis (RR=0.2309,P=0.012), preoperative pyridostigmine dose (RR=0.4349, P=0.016), thymoma (RR=0.0606, P=0.000), and major postoperative complications (RR=0.1094, P=0.000) were significantly related to postoperative myasthenic crisis.Multivariate Logistic regression analysis showed that Osserman stage (Ⅱb+Ⅲ+Ⅳ) (RR=0.0953, P=0.000), thymoma (RR=0.0294, P=0.000), and major postoperative complications (RR=0.0424, P=0.000) independently predict postoperative myasthenic crisis.Conclusion Osserman stage (Ⅱb+Ⅲb+Ⅳ), thymoma and major postoperative complications are independent predictors of postoperative myasthenic crisis in patients with myasthenia gravis who underwent thymectomy.