Objective To observe the curative effects of cyclophosphamide treatment in myasthenia gravis（ MG） with thymoma and adverse reactions in the treatment. Methods A total of 50 cases of myasthenia gravis patients that had proved thymoma by pathology after thymectomy were given cyclophosphamide sequential therapy. Cyclophosphamide was given intravenously at a dose of 0.20 g/d（ twice a week）， gradually increased to 0.80 g/d（ once a week） till the total dose was 10 g， and continued at a dose of 0.80 g/d（ once a month） until the total dose was 20.4 g. The severity and efficacy of myasthenia were evaluated according to clinical absolute score and relative score， and adverse drug reactions were observed. Results Compared with the clinical absolute scores of prior treatment（ 20.44±8.80）， when the total treatment dose reaches 6 g， 10 g， 20.4 g， the clinical absolute scores were（ 14.20±8.68），（ 10.96±8.27） and（ 3.84±4.44） respectively， which were significantly reduced（ P ＜ 0.05）. Comparing the clinical absolute scores of the total dose 6 g and 10 g with 20.4 g， the difference was statistically significant（ P＜0.05）. The effective rate of 50 cases at the total dose 6 g， 10 g and 20.4 g were 70%， 78% and 94% respectively. With the increase of the cyclophosphamide dosages， the curative effect was more obvious， and the adverse reactions were mild and tolerable. Conclusions The curative effect of cyclophosphamide medicine for MG with thymoma is obviously. The greater the total dose， the better the curative effect. When cyclophosphamide total dose reaches 20.4 g， the curative effect is remarkable with less adverse reactions. It was worthy of recommendation.