The 1928 United States Senate election in Wisconsin was held on November 6, 1928.
Incumbent Republican U.S. Senator Robert La Follette Jr., who had won a special election to finish his late father's term in 1925, was elected to a full term in office.
La Follette had to fend off two challenges from his own party, defeating George W. Mead in the party primary and Republican State Senator William H. Markham in the general election. Markham ran as a pro-Hoover "Regular Republican."
The Democratic Party of Wisconsin decided to endorse the progressive La Follette after he won the Republican primary. The Democrats asked their own nominee, Michael K. Reilly, to withdraw from the race; he agreed, announcing his decision on October 8. This was part of a broader attempt at a coalition between progressives and Democrats in Wisconsin to throw the state to Democrat Al Smith in the concurrent presidential election.