The Yeji building is the main building of Seoul Science High school. It is placed in the center of the school, and is a four-story building. The building is named after the school motto, "Yeji" which means "manners and wisdom". The first floor is mostly occupied with departments for the management of the school such as the administration office, and the principal's office. There are also valuable scientific instruments such as the Wind Tunnel and 3D printer, and classroom about invention at the first floor. The second floor is for Earth science; it has laboratories and lecture rooms. It also has a study hall which connects the Yeji building to the library and the Fusion talent building. The study hall allows the students to do their work in their free time and the study hours after school. There is also a small classroom where students can use their laptops for researching and making presentations. The third floor has a gym and lecture rooms, laboratories for physics. There are instruments such as the high-speed camera and the forward-looking infrared. There are laboratories and lecture rooms for biology and room for SEM on the fourth floor. The biology laboratory is full of scientific instruments. There is an observatory on the rooftop which the largest telescope in Seoul. There are three telescopes for taking pictures of the large-scale structures of the cosmos and a planetarium bought in the 1990s.