Abstract : Platelet indices correlated with cardiovascular risk factors and mortality in children with congenital heart disease (CHD). Cyanotic CHD usually had a low platelet count with a high level of other platelet indices. This study evaluated the difference in platelet indices between cyanotic and acyanotic CHD undergoing cardiac catheterization. A retrospective study evaluated children with CHD, age 1 month until 18 years, hospitalized at Dr. Soetomo General Academic Hospital, Surabaya. Children were classified into acyanotic and cyanotic CHD based on echocardiography result and cyanotic signs. They undergo diagnostic or therapeutic catheterization procedures from January 2020 to December 2021. Platelet count, mean platelet volume (MPV), platelet crit (P-PCT), platelet large cell ratio (P-LCR), and platelet distribution width (PDW) were markers of platelet indices, examined by Hematology Analyzer SYSMEX XN 1000 from peripheral blood sampling. We used the independent sample t test to differentiate the mean of platelet indices between acyanotic and cyanotic CHD with a significance level of p<0.05 (two-tail test). There were 208 from 258 children had complete data. About 61(29.3%) were cyanotic CHD, and 147(70.7%) were acyanotic CHD. Boys in cyanotic CHD was more prevalent than in acyanotic CHD (65.6% vs 39.5; p=0.001). Diagnostic catheterization was performed in 94(45.2) % of children, and therapeutic catheterization was in 114 (54.8%) children. Platelet count was similar between cyanotic and acyanotic CHD (p=0.434). Thrombocytosis with a platelet count above 450.000/mm3 occurred in 16.4% cyanotic CHD and 8.8% acyanotic CHD. The P-PCT had no significant differences between cyanotic and acyanotic CHD. The mean PDW, MPV and P-LCR in acyanotic CHD were lower than in cyanotic CHD; 9.5(SD=1.57) fL and 10.9(SD=2.41) fL with p<0.001; 9.3(SD=0.79) and 9.8(SD=1.4) fL with p=0.007; 19.1(SD=6.11) and 23.0(SD=8.52) with p=0.002; respectively. Platelet indices in cyanotic CHD were higher in cyanotic CHD than acyanotic CHD, especially for PDW, MPV and P-LCR.