The west African country’s newly elected president -- who has become known as the “Iron Lady” -- dismissed the staff during a visit to the ministry on Wednesday.
"All employees of this ministry are hereby dismissed, and will have to apply to come back if they wish," she said.
"The ones that will be accepted will be those who have the competence of being employees of this sensitive ministry," she told reporters.
Responding to one employee who complained that they could not be fired on the spot because they are civil servants, Ms Sirleaf said they were all political appointees.
An official from the ministry who asked not be named, estimated the number of workers affected by the dismissal order to be 300.
Ms Sirleaf, who vowed during her inauguration ceremony to "wage a war against corruption regardless of where it exists", told reporters the measures she took at the finance ministry were the first step towards keeping her pledges.
"If we are to achieve our economic and income distribution goals, we must take on forcibly and effectively the debilitating cancer of corruption," she said in her inaugural address last month.
Ms Sirleaf, whose government is under the international spotlight after 14 years of successive and brutal wars, has promised to abide by conditions of a governance and economic management program (GEMAP) aimed at tackling the serious economic and financial irregularities that had become commonplace.
"This ministry has embarrassed our country a lot with the international community because of the corrupt practices that have been taking place here," she said.
The veteran economist-turned-president said the key ministry had to be run by competent people with financial management training.
On Tuesday, Ms Sirleaf ordered officials of the transitional government whose term ended when she took power to stay in the country during an audit of their offices.
The audits were consistent with government policy of ensuring accountability and transparency, the president’s office said, amid reports of outgoing government officials looting cars and grabbing office equipment and furniture.
The Liberian leader promised that only those who have a basic training in financial management will be re-hired "and the government will provide training opportunities to improve their skills."
"If you don't have the right people in the rightful positions there will always be problems," she said.
Former employees vowed to challenge the sacking decision legally.
"She has done her own and we will do ours," one former employee, Robert Bryant, told news agency AFP.
"Government owes us months of arrears, we have family to feed, and how are we going to manage it? This is not the way to take decisions," he said.
President Sirleaf inherited a bloated and poorly paid public service for which there are salary and benefit arrears totalling about US$20 million (A$26.5 million).