She adds that "In the name of ... Christ, I quit Christianity and being Christian. Amen."
Her publisher, Alfred A. Knopf, confirmed Thursday that the posting was by Rice.
Rice is best known for "Interview With a Vampire" and other gothic novels. Raised as a Catholic, she had rejected the church early in her life, but renewed her faith in recent years and in 2008 released the memoir "Called Out of Darkness: A Spiritual Confession."