PITTSBURGH (AP) _ The last general-interest movie house in downtown Pittsburgh has shown its last picture show.

The Fulton Mini on Sixth Street closed Tuesday night, its owners said, leaving only an X-rated theater and an art house downtown.

''It's bad enough when a theater closes,'' said George Stern of Cinemette Corp. ''There is no use making a big blast about it.''

Co-owner Ernest Stern said downtown theaters are not profitable because of the rise of theater complexes in suburban shopping malls.

The Fulton Mini, along with three other Cinemette theaters that closed last summer, lost a total of $250,000 from September 1985 to September 1986, George Stern said.

Still open downtown are the Fulton I, owned by Cinemette, which shows foreign and art films, and the independent Art Cinema, which shows X-rated films.