Purpose: I did this tudy to know whether its epidemiological eatures were different in terms of the antigenic type. Methods: I collected and investigated the epidemiological and demographic informations of influenza patients who had visited and been diagnosed at the Department of Pediatrics and mergency room , Yogin Severance Hospital from June 2016 to May 2018 under 18 years old. They were grouped by antigenic type as well as detection time. Results: Their mean age and male to female ratios were 7.1±4.4 years old and 255:199 for influenza A and 6.9±4.1 years old and 109:88 for influenza B and there was no significant difference between them. The case numbers for influenza A and influenza B were 345 cases and 12 cases during season A(June 2016~May 2017) and 116 cases and 185 cases during season B (June 2017~May 2018), respectively. The antigenic predominance were different between the two seasons (P <0.001). Influenza A cases showed a significant seasonal age difference (7.8±4.4 years old for season A vs. 4.8±3.6 years old for season B, P <0.001) and influenza B cases did not (8.7±5.6 years old for season A vs. 6.8±4.2 years old for season B, P =0.143). Seasonal age difference between the two types was present during season B (P <0.001), not during season A (P =0.569). Monthly ages for influenza cases were significantly decreased from December 2016 (8.1±4.3 years old) to January 2017 (4.7±4.0 years old) (P <0.001), but not during other period and there was no significant difference among monthly ages in influenza B cases. Monthly age differences between the two types were remarkable during early period of season B.Conclusion: The antigenic type predominance has changed by season. Significant seasonal and monthly age changes in influenza A and the age difference between the two types during season B have occurred. These findings verify the necessity of continuous monitoring for them and should be applied to the making the influenza prevention policy.