The Mainstreet Theater, also commonly referred to as The Empire Theater, is a historic theater located at 1400 Main Street in downtown Kansas City, Missouri. The theater was landmarked and placed on the National Register of Historic Places in February 2007.
Designed by Rapp & Rapp, the 90,000-square-foot (8,400 m2) theater opened on October 30, 1921 as the Mainstreet Missouri. The 3,200 seat theater was a popular vaudeville and movie house, and the only theater in Kansas City designed by Chicago firm Rapp and Rapp. The interior of the theater was designed in French Baroque style, and the exterior is a blend of neoclassical and French Second Empire. The lobby is topped by a dome encircled by circular windows. The Mainstreet Theater was the largest theater in Kansas City until the Midland Theatre opened in 1927.
The name of the Mainstreet Theater changed to the RKO Missouri Theater in April 1941. The RKO Missouri ran Cinerama three strip film.