The high court on Monday refused to hear an appeal from Michael Newdow, who argued that government references to God are unconstitutional and infringe on his religious beliefs.
Many presidents have added "so help me God" to the oath.
Newdow sued to keep Obama from doing so and lost. He wanted overturned an appeals court's ruling saying it would be useless to ban Chief Justice John Roberts from prompting Obama to say "so help me God" because the president could have easily found someone else to administer the oath.
The case is Newdow v. Roberts, 10-757.