He will receive five weeks of basic military training as part of his 21 months of mandatory military service.
Before his entry into an Army replacement depot in Shinbuk-myeon, Chuncheon, Gangwon Province, about 500 of his enthusiastic fans at home and abroad gathered there to say goodbye to Eunhyuk.
Xu Yan, a 23-year-old woman from Hong Kong, said: "I waited for him here from 5 a.m. I feel sad that I will have to miss him for about two years, but I can wait for him until that time."
In South Korea, all able-bodied men are subject to about two-year mandatory military service.