King David Kalakaua Building, Federal courthouse in Honolulu, United States.

The King David Kalakaua Building is a government building at 335 Merchant Street in downtown Honolulu, designed in 1918 and built from 1921 to 1922 in Mission/Spanish Revival style. A 1929 addition opened in 1931. It served as the federal post office, customhouse and courthouse, holding courtrooms and offices for the U.S. District Court for the District of Hawaii.

Construction took place from 1921 to 1922 as a post office, customs facility, and courthouse, with a major expansion completed between 1929 and 1931. The building's transition to state control in 2003 marked a significant change in its administrative purpose and governance.

The building was renamed in December 2003, when the federal government sold most of it to the state of Hawaii for US$32.5 million; the new name honors David Kalākaua, the last king of the Hawaiian monarchy. A small section still operates as a post office, so mail and the building's former federal role share the same address.

The building now houses the Hawaii Department of Commerce and Consumer Affairs along with a postal services section. As an active government office, access may be restricted and security procedures should be expected when visiting.

A small section of the building still operates as a post office, decades after federal agencies moved to the Prince Kuhio Federal Building near Honolulu Harbor. The rest of the 1921–22 structure, expanded in 1929–31, now holds the Hawaii Department of Commerce and Consumer Affairs.