The swearing in ceremony was held at the Kelaniya Rajamaha Viharaya and Mr. Rajapaksa was sworn in at the auspicious time of 9.32.
This is the fourth time Mr. Rajapaksa was sworn in as Prime minister of Sri Lanka.
He secured the highest number of preferential votes at the recently concluded General election.
Meanwhile, the new cabinet of ministers is to be sworn in on Aug. 14 at the historic city of Kandy.