The 320 South Boston Building, formerly known as the National Bank of Tulsa Building, is a 22-story highrise building located in downtown Tulsa, Oklahoma. It was originally constructed at the corner of Third Street and Boston Avenue as a ten-story headquarters building for the Exchange National Bank of Tulsa, Oklahoma in 1917, and expanded to its present dimensions in 1929. The addition brought the building's height to 400 feet (122 m), making it the tallest building in Oklahoma.