The 1990 United States Senate election in Iowa was held on November 5, 1990. Incumbent Democratic U.S. Senator Tom Harkin sought re-election to a second term in office. Harkin was opposed by Republican U.S. Congressman Tom Tauke, from Iowa's 2nd congressional district, and both Harkin and Tauke won their primaries uncontested. Though Harkin performed slightly worse than he had six years earlier, he was successful in his re-election bid and defeated Tauke. He was the only Democrat re-elected to the Senate from the state since 1938.