The hand-written notes sold in Los Angeles for just under £250,000.
They included his view on the subject of God, in one he wrote: "I have repeatedly said that in my opinion the idea of a personal God is a childlike one."
But the 27 letters suggest Einstein did believe in God, after declaring himself an agnostic.
The letters are reported to talk about a number of topics, including his thoughts on the Atomic Bomb and the rise of Hitler and Nazism.
Speaking in the Telegraph newspaper, Chief Executive of Profiles in History auction house, Joseph Maddalena said these letters were "an embodiment of his life's work".