320 South Boston Building, Beaux Arts skyscraper in downtown Tulsa, Oklahoma, United States

The 320 South Boston Building is a 22-story Beaux Arts skyscraper on Boston Avenue in downtown Tulsa, spanning a full block between Third and Fourth Streets. It is clad in brick with terra cotta trim, and its lower two stories are entirely terra cotta. The central tower steps back at the 20th floor into a two-story arcade, topped by a temple-fronted section and a cupola.

The Exchange National Bank of Tulsa built a ten-story headquarters here in 1917, designed by Oscar Wenderoth of Chicago's Weary & Alford Company. A 1929 expansion brought it to 22 stories and 400 feet (122 m), making it Oklahoma's tallest building until 1931 and Tulsa's tallest until 1967. The bank reorganized as the National Bank of Tulsa in 1933, and the building took its present name after BOK moved out in 1977.

The building's name tracked its main bank: Exchange National Bank, then National Bank of Tulsa from 1933, and 320 South Boston after Bank of Oklahoma moved out in 1977. Hall Estill, one of Oklahoma's largest law firms, is among current tenants. A tunnel under South Boston Avenue links it to the Kennedy Building.

Visitors can view the building from outside and explore the nearby underground access points that connect to surrounding amenities. The area makes it easy to move between the structure and nearby services without going above ground.

A persistent local myth held that the building's pinnacle was designed as a mooring mast for airships, and that a U.S. Navy zeppelin tied up there in the 1930s. The story was repeated by local media but is false. In 1949 the KOTV television station put its first transmitter on the roof; a falling wrench during the work killed a woman in the street below.