The fire spread extensively across the landmark which is popular with walkers and tourists and producing smoke visible from miles around.
Arthur's Seat is the highest point of Holyrood Park, near Scotland's parliament and the end of Edinburgh's famous Royal Mile. About 250m above sea level, it is a popular vantage point with visitors for its views of the city.
"Crews are in attendance at a fire in the open at Arthur's Seat, Holyrood Park, Edinburgh," the Scottish Fire and Rescue Service said on X.
Police advised motorists and pedestrians to avoid the area.
August is a popular month for tourists in Edinburgh as it hosts the Edinburgh International arts festival, the Fringe comedy festival, as well as tour dates for the reunion of rock band Oasis.
