L-tetrahydropalmatine (Rotundium) is an alkaloid of Corydalis turtschaninovii. Some animal experiments had demonstrated that Rotundium had a good antiarrhythmic effect in blocking the calcium channel and that it was a class IV antiarrhythmic agent, similar to that of Bepridil in literatures. This is a clinical report of Rotundium (oral given) on an atrial fibrillation (AF) patients. The therapeutical results were evaluated by 24 hours ambulatory electrocardiographic monitoring and ECG. The results showed that the effective rate of Rotundium on paroxysmal atrial fibrillation and sustained atrial fibrillation of 45 mm (left atrium diameter) or more was 30%, while LAD of less than 45 mm was 80% (P < 0.01). Among 8 cases' duration of AF were 6 months or more, 3 cases were effective, the effective rate 37.5%, while among 10 cases' duration of AF were less than 3 weeks, 3 cases were converted to sinus rhythm, 5 cases were effective. There was a significant difference between two groups. Age and sex exerted no effect on efficacy. During taking Rotundium, blood pressure had no apparent changes and no severe side effects were found. The results showed that Rotundium is an effective, safe new drug to treat AF, especially in paroxysmal atrial fibrillation. The antiarrhythmic mechanism of Rotundium might be related to its prolonging of the effective refractory period of atrial and atrioventricular node.