The building of the Mixed Department of Morozov Children's Hospital is located in the left row of pavilion buildings, which also included the buildings of the Scarlet Fever, Diphtheria, and 2nd Infectious Departments, as well as the hospital chapel (which has not survived). This two-story building was constructed in the early 20th century according to the design of architect I.A. Ivanov-Shitz in the Art Nouveau style.

The Mixed Department, intended for patients with various diagnoses, opened in early 1904. It included three separate wards: for patients with scarlet fever and diphtheria (15 beds on the second floor); for patients with scarlet fever with measles; for patients with diphtheria with measles (both with 15 beds on the first floor). Each ward had three rooms, a buffet, a toilet, a bathroom, and laundry rooms. The building also housed a common laboratory for all three departments.

Like in other buildings of Morozov Children's Hospital, patients in the Mixed Department enjoyed all the conveniences of the time: central steam-water heating, ventilation, and electricity. High ceilings (over 4 meters) created a sense of spaciousness, while large windows provided good lighting. The floors in the wards were made of oak parquet.

The two-story building of the Mixed Department, with its symmetrical facade, resembles a small palace and is one of the most expressive buildings in the hospital complex. It was not plastered, and the white stone decorative elements stood out strikingly against the red brick walls. The facade decor has been well preserved.

The central part of the facade with the main entrance is highlighted by a small vestibule-rizalite, above which rises an attic. The building is crowned by a symmetrical composition of chimneys: two in the center of the facade and two on the flanks of the second floor. The main facade is characterized by a strict rhythm of paired vertical windows. The side parts of the building (two axes each) were single-story, while the opposite facade had wide single windows.

During the Soviet era, the side single-story parts of the building were raised to a second floor. This somewhat changed the silhouette of the building but did not disrupt its style and perception as an architectural monument.