1898 United States Senate elections in Ohio

On January 12, 1898, the Ohio General Assembly met in joint convention to elect a United States Senator. The incumbent, Mark Hanna, had been appointed by Governor Asa Bushnell on March 5, 1897, to fill the vacancy caused by the resignation of John Sherman to become Secretary of State to President (and former Ohio governor) William McKinley. Hanna's appointment was only good until the legislature met and made its own choice. The legislature elected Hanna over his fellow Republican, Cleveland Mayor Robert McKisson, both for the remainder of Sherman's original term (expiring in 1899) and for a full six-year term to conclude in 1905.

Hanna, a wealthy industrialist, had successfully managed McKinley's 1896 presidential campaign. The Ohio Republican Party was bitterly divided between the faction led by McKinley, Hanna and Sherman, and one led by Ohio's other senator, Joseph B. Foraker. Bushnell was a Foraker ally, and it was only under pressure from McKinley and others that he agreed to appoint Hanna to fill Sherman's Senate seat. After Hanna gained the appointment, Republican legislators kept their majority in the November 1897 election, apparently ensuring Hanna's election once the new body met in January 1898. However, before the legislative session, the Democrats allied with a number of Republicans, mostly from the Foraker faction, hoping to take control of the legislature and defeat Hanna.

The coalition was successful in taking control of both houses of the legislature; with the Senate election to be held just over a week later, intense politicking took place. Some lawmakers went into hiding for fear they would be pressured by the other side. The coalition decided on McKisson as their candidate the day before the balloting began. Three Republican state representatives who had voted with the Democrats to organize the legislature switched sides and voted for Hanna, who triumphed with a bare majority in both the short and long term elections. Bribery was alleged; legislative leaders complained to the United States Senate, which took no action against Hanna. McKisson lost a re-election bid as mayor in 1899; Hanna remained a powerful figure in the Senate until his death in 1904.