Objective: To verify efficacy and safety of radiofrequency catheter ablation (RFCA) in very young children. Methods: We reviewed the records of a total of 203 patients (aged 10 months to 37 yr) who had undergone RFCA, from March 2000 to June 2008. The results of RFCA in young children group(≦ 6 years old, n=33 )were compared to those in older children group(≧7 years old, n=170 ). Results: In young children group, disease distribution, success rate and recurrence rate were as follows: atrioventricular reentrant tachycardia (AVRT, 69.7%, 91.3%, 0%), ectopic atrial tachycardia (EAT, 9.1%, 100%, 0%), permanent junctional reciprocating tachycardia(PJRT, 9.1%, 100%, 33.3%), atrioventricular nodal reentrant tachycardia(AVNRT, 6.1%, 100%, 0%), junctional ectopic tachycardia (JET, 3%, 100%, 0%), atrial flutter(AFL, 3%, 100%, 0%). In older children group, disease distribution, success rate and recurrence rate were as follows: AVRT(61.8%, 98.1%, 2.9%), AVNRT (25.9%, 100%, 0%), ventricular tachycardia (VT, 7.6%, 100%, 0%), AFL(2.4%, 50%, 25%), EAT(1.8%, 100%, 0%). There was valuable difference of disease distribution between two groups (p<0.001). The overall success rate of RFCA in younger group (90.9%) was not different to older group (97.6%) (p=0.97). In older children and young adult, incisional atrial flutter showed the lowest success rate and the longest fluoroscopy time. There was no valuable difference of recurrence about types of arrhythmia between two age groups. There was 1 major complication of complete heart block requiring permanent pacemaker in older children group who had concealed parahisian accessory pathway. Conclusion: In young children, RFCA was as effective and safe as in older children. Therefore for highly symptomatic tachycardia in this age group, RFCA can be considered as curable treatment modality.