Police have said that there's a "clear pattern" linking all of the incidents in St Landry Parish near the capital, Baton Rouge.
"We do believe that this fire is suspicious," Louisiana State Fire Marshal H Butch Browning told local reporters.
"We do believe a crime has occurred."
The first fire occurred on 26th March at St Mary Baptist Church (pictured below), with two more taking place over the past week.
Pastor Harry Richard from Greater Union Baptist is the grandson of a man that helped start the church more than 100 years ago.
He explained why the damage is personal: "He left a legacy for me and I was trying to fulfil that to the best of my ability."
All the fires were begun in the middle of the night when the churches were empty.
Security has been beefed up at other churches in the area.
Historically, the burning of black churches was used to intimidate communities and parishioners and has been taking place particularly in southern states for decades.
In June 2015, Dylann Roof shot and killed nine black church members in Charleston, South Carolina.
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