【Background】Infants with congenital heart diseases (CHD) are at high risk of RSV infection, which may cause severe respiratory distress, rarely death, and probably reactive airway diseases at follow-up period. In 2005 Oct. Palivizumab was approved for infants < 2 y/o with CHD in Japan. We conducted surveys using questionnaires to assess usage, prophylactic efficacy, and safety of Palivizumab in Japanese infants with CHD pre and post approval period. Although several indications have been made in US and EU, we have made an original treatment guideline including hemodynamically significant CHD, heart failure due to cardiomyopathy, association with respiratory disorders, and symptomatic and clinically significant arrhythmia, in the scientific committee of JPCPS. Age was < 2 y/o.【Results】In 2004 Oct., Japanese first trial started and demonstrated incidence of hospitalization due to RSV: 4.5% (3/67) and of on-respirator: 1.5% (1/67). The data were comparable with data from USA: 5.3% for hospitalization, 1.3% for on-respirator. Relative reduction rate of RSV infection was -45.3%. Post approval surveillance was performed from 2005 Oct. to 2006 Mar., RSV breakout season in Japan. Total case surveyed was 4,918. Infants matched for Japanese GL were 1,465 (29.8%). Among them, Synagis was injected in 1026 infants (70%). As a result, the incidence of RSV infection was 2.53% (29/1,148), compared with 4.42% without Palivizumab but matched for guideline, and 0.43% without guideline. Relative reduction rate of RSV infection was -42.8%.【Conclusions】From the post marketing survey, Palivizmab was used in 70% of Guideline-matched infants. Guideline-matched infants have higher infection rate, longer hospital period, higher incidence of oxygen and respirator use. Relative reduction rate of RSV infection by Palivizmab was 42–45%. Palivizumab is well-tolerated in children with CHD, and adverse events were not severe. Palivizumab is effective and safe in preventing or alleviating RSV infection in infants with CHD.