Aims: To evaluate the safety and efficacy of a new approach for transseptal catheterization in patients undergoing percutaneous balloon mitral valvuloplasty (PBMV). Methods: One hundred and two patients with rheumatic mitral stenosis were randomized into two groups. In the study group (RA approach), an imaginary horizontal line was drawn from the top end of the tricuspid valve under anteroposterior fluoroscopic view. The intersection of the horizontal line and the right edge of the corresponding thoracic vertebra was defined as the upper border of the Fossa ovalis. The atrial septum was punctured from a point 0.5 cm below the upper border of the Fossa ovalis. In the control group (LA approach), an imaginary horizontal line was drawn between the upper and middle third of the left atrium, and the intersection of this horizontal line and the right edge of the corresponding thoracic vertebra was used as an atrial septum puncture point. Results: Atrial septum puncture succeeded in all patients in the study group and in 72.6% of the patients in the control group (p < 0.01). The average fluoroscopy times for transseptal catheterization in the study and the control groups were 2.0 ± 0.5 and 3.0 ± 1.0 min, respectively (p < 0.01). Transseptal catheterization was subsequently achieved using the RA approach in the 14 patients from the control group in whom the LA approach failed. Conclusions: The RA approach is a safe and effective means for transseptal catheterization in patients undergoing PBMV.