Background: Modified Blalock-Taussig shunt using 3mm or 3.5mm PTFE graft has been performed in patients with small body weight or in candidates for single ventricle palliation. However, there are few reports concerning clinical outcomes in terms of pulmonary artery growth and shunt patency rate after shunt operations using such a small graft. Material and Method: Twenty-five patients rate after shunt operations using 3 or 3.5 mm sized grafts from September 1996 to August 1999. We retrospectively assessed the pulmonary artery growth and the shunt patency rate by reviewing the pre-and post-operative pulmonary angiograms. The risk factors for late death and second shunt operations were also analyzed. To assess the presence of any correlation between body weight and selection of the graft size, regression analysis was done in 81 cases of shunt operations performed during the same period. Result: There were 1(4%) early death and 5(20%) late deaths. The survivors were followed up for an average of 7.34 months. The pulmonary artery index increased significantly from 129$pm$66$ extrm{mm}^2$/$m^2$ to 213$pm$114 $ extrm{mm}^2$/$m^2$(p=0.002). The shunt patency rate assessed at postoperative 2, 4, 6 and 8 months were 82.5%, 77%, 73% and 42% respectively with a marked decline between 6 and 8 months. Asplenia was a frequent finding for the patients with late death although the incidence failed to reach statistical significance(p=0.078). Pre-operative diagnosis of PA with VSD was found to be a statistically significant risk factor for a second shunt operation(p=0.01). Body weight(a) at operation and graft size(b) used in the shunt operations revealed strong correlation and could be expressed by the following formula; b=0.128a + 3.233. Conclusion: Adequate growth of pulmonary artery and satisfactory early patency rate could be obtained by modified Blalock-Taussing shunt using 3mm or 3.5mm graft. However, during 6 to 8 months after shunt operations, the patency rate fell sharply, which implicates that close observation and early intervention are mandatory in this period.