After an unsuccessful attempt, the members of the ";Rikánbelőli"; community finally managed to establish a Hungarian high school in Háromszék, in the late 1850s, with the help of Ferenc Gödri, Ferenc Kemény and count Imre Mikó.
The school was chosen to be built in Saint George thanks to the financial support provided by the town. The first classes were based next to the Calvinist church in the year of 1859. Sándor Vajna, the only qualified teacher was appointed as headmaster.
In 1863 the school moved to its present place, the city centre. In 1870, after Gusztáv Zofalh’s plans the construction of the oldest wing of the present building was started. Later, count Imre Mikó donated a considerable amount of money for the further development of the institution. That is why the school was named after him till 1948. After a remarkable improvement, the school could afford 3 qualified teachers and the south wing was also constructed after Ignác Alpár's plans.
In 1893 the year of the first graduation. The school underwent a great development until the World War I: the number of students was increasing steeply, more and more teachers were employed. The locals were supporting the introduction of more facilities in order to offer education in Hungarian for all the students in the region. Headmaster Vilmos Csutak had an important role in this process.
The damages caused by the world wars and a strong earthquake in 1940, the school was forced to stop teaching till 1944. After that it was taken into public ownership, the name of it was changed many times because of the political system in the country. From 1989 the school wears again the name of ";Székely Mikó Kollégium";.
During Communism the school has gone through some important changes: the furniture was changed, the gym was modernized, new blocks of buildings were constructed with new classrooms, a kitchen and canteen. In 1973 the Jókai buliding was started to be used as school workshop.
The earthquake in 1977 caused serious damages, the teaching had to be moved to other buildings, but in 1978 it was repaired and the edducation could be continued.
From 1989 the students can study art subjects besides the existing scientific education. It is a prioroty to keep its traditions and build twinned school partnerships. Students participate in international competitions all around the world. Nowadays there are more than 1200 students and more than 60 teachers.
The 150-year-old institution is the biggest and the most successful Hungarian highschool in Háromszék region.