The Republican filed paperwork Monday morning which allows him to open a campaign committee and begin raising money for a run in 2010.
That's when Brownback's second Senate term is up. He's always said he would not seek a third.
"I will continue to work hard during the coming year in the Senate to find solutions to the serious issues facing our state and the nation and focus on efforts to create jobs at home and grow our Kansas economy," Brownback said in a statement.
Democrat Kathleen Sebelius is prohibited from running again for the Governor's office. Secretary of State Ron Thornburgh has also expressed interest in seeking the Republican gubernatorial nomination.