The gadget was added on Tuesday to the list of prohibited photography accessories forbidden at the 19 museums and one zoo managed by the institution.
In an announcement posted on its website, the Smithsonian cited safety concerns.
"This is a preventive measure to protect visitors and objects, especially during crowded conditions," the notice said.
More than 26 million people visited Smithsonian locations in 2014. They can still capture selfies, just without the unwieldy tool.
"We encourage museum visitors to take selfies and share their experiences—and leave the selfie sticks in their bags," the announcement said.