Purpose : Tuberculosis, a major public health problem, is an important cause of childhood infectious diseases. To decrease the tuberculosis morbidity rate, BCG vaccination and chemoprophylaxis are performed. Recently 2TU PPD skin test was introduced as a diagnostic method for tuberculous infection. We studied the positive conversion rate of 2TU PPD test after percutaneous multiple puncture BCG vaccination. Methods : Four hundred seventy six infants from well baby clinic of Samsung Cheil Hospital were enrolled. They were immunized with percutaneous multiple puncture technique BCG(Japan BCG laboratory, Japan) at 1 month of age. Approximately 6 months later, tuberculin skin test using RT23 2TU PPD was performed. Induration size, family history of tuberculosis and number of BCG scars were evaluated. Induration greater than or equal to 5mm was defined as positive conversion. Results : Among 476 infants, 248(52.1%) were male and 228(47.9%) were female. PPD skin tests were performed $6.2{pm}0.5$($mean{pm}S.D.$) months after BCG vaccination. Mean induration size was $7.3{pm}3.2mm$ and positive conversion rate was 85.5%. Total number of BCG scars was $15.5{pm}3.2$. Conclusion : The seroconversion rate by 2TU PPD test after percutaneous multiple puncture BCG vaccination was high. But, more comparative studies with various age groups may be needed for 2TU PPD test used as diagnostic method of tuberculosis in the hospitals.