BACKGROUND We present a rare case of prolonged neuromuscular blockade and insufficient reversal after sugammadex administration in a pregnant patient being treated with magnesium sulfate and nifedipine undergoing cesarean section under general anesthesia. METHODS A 37-year-old woman at 34 weeks gestation, weighing 42.5 kg, and receiving magnesium sulfate 94 mg/kg for preeclampsia and nifedipine 20 mg, underwent cesarean section under general anesthesia for abruptio placentae. Her trachea was intubated after administering rocuronium 0.94 mg/kg. Postoperatively, sugammadex 4.7 mg/kg was administered at post-tetanic count 2, 163 min after rocuronium administration. However, 9 min after sugammadex administration, the train-of-four ratio only reached 0.7. Fifteen min after sugammadex administration, extubation was successfully performed when the train-of-four ratio reached 0.9 after administration of atropine 0.5 mg and neostigmine 1.0 mg. CONCLUSIONS Caution is required in pregnant women on high-dose magnesium sulfate with nifedipine, which may cause prolongation of neuromuscular blockade and insufficient reversal.