PURPOSE: To investigate the spontaneous closing time of PDA in term and preterm infants without respiratory distress syndrome. METHOD: For twenty four term and sixteen preterm infants without RDS, prespective echocardiography was performed within 24hr of birth, which was repeated everyday till spontaneous closure of ductus. At the same time, LA/Ao ratio in M-mode echocardiography and blood pressure were checked. RESULT: In term infants, spontaneous ductal closure rate was 15% in the first day of life, 57.7% in the second day, 88.5% in the third day, and 100% in the fourth day. For the preterm infants without RDS, the spontaneous ductal closure rate was 25%, 73.3%, 86.7%, 93.3% in each day. One preterm infant dided of meningitis at second day of life was excluded. One preterm infant (11,23 who had patent ductus arteiosus at fourth day of llife showed persistent ductus at 6 months of life. CONCLUSION: Spontaneous closure of patent ductus arteriosus will not occur if there is persistent shunt after 4th day of life in term and preterm infants without RDS.