The behavior included Slater allegedly making derogatory comments toward African-American employees.
According to the network, the allegations had come to light in recent weeks.
The incidents were reported to Fox News' HR chief Kevin Lord within the past two months.
According to a source familiar with the matter, Slater, who has worked for the media giant 19 years, was terminated within two weeks.
"We take any complaint of this nature very seriously and took the appropriate action in investigating and firing Ms. Slater within two weeks of this being brought to our attention," Fox News said in a statement.
The statement added that there is no place for abhorrent behavior at Fox News.
This is the latest drama for the Fox News Channel. In July, the corporation was rocked when chief Roger Ailes left amid allegations of sexual harassment.
Since that episode, the company's parent, 21st Century Fox, has reached financial agreements with former 'Fox and Friends co-host Gretchen Carlson, and others who made several sexual harassment complaints.
The individuals who were compensated also spoke of a disturbing culture and tone that permeated the organization.
Recently, former on-air contributor, Tamara Holder, reached a settlement with the network worth more than $2.5 million. This was after she claimed that Fox News Latino Vice President Francisco Cortes sexually harassed her.
Cortes was terminated.
Andrea Tantaros, former 'The Five' co-host, filed a $50 million sexual harassment suit in August 2016.
The case is still pending.