"On behalf of the American people, the president congratulates His Majesty King Philippe on the occasion of his investiture as King of the Belgians," the White House said in a statement.
Philippe, 53, was sworn into office by the joint houses of parliament shortly after Albert,79, stepped down, citing failing health.
The White House said: "The president also sends his heartfelt appreciation to King Albert II for his warmth, service and leadership as he steps down after nearly 20 years.