The station building was designed by the Belgian architect Jean-Pierre Cluysenaar in 1852 and was officially inaugurated on 6 July 1856 by Crown Prince Leopold, later King Leopold II. The architectural style of the station building is a mix of a medieval castle with a Gothic town hall. The building was built in Boomse papensteen and bluestone, reminiscent of Tudor Gothic. The two side pavilions and the awning on the platform side were added in 1890.
In 1975 the building was "worn out" and a demolition request was submitted on August 26, 1975. Due to its unique (historical) character, various authorities and associations insisted on preserving the outdoor area. A Royal Decree of 19 June 1978 ensured the protection of the old station building and the surrounding area. In September 1990 the station building was nevertheless demolished, but without touching the outer walls and the tower. It is Jean-Pierre Cluysenaar's only "station de ville" that still exists. The stations of Ninove and Geraardsbergen were completely demolished to make way for a single-storey new building.
A scale model of the Aalst station can be viewed in the premises of the East Flemish Model Building Association in Aalst.
At the end of 2001, the city of Aalst, De Lijn, the NMBS, the Post and NV Amylum joined forces to thoroughly embellish the Aalst station environment (Project ASO).