A police spokesman said: "The woman in her 60s has been arrested on suspicion of arson with intent to endanger life. She is currently in custody in Melksham."
A blaze broke out in a house in Little Somerford this morning and fire crews and police are still at the scene.
A police spokesman said: "We are currently assisting the fire service with a house fire in Little Somerford, near Malmesbury.
"Nobody has been injured and everybody is out of the property, but there is a road closure in place between Meadow Lane and Park Lane, in Great Somerford.
"Please avoid the area and find alternative routes."