The Prime Minister was received by his Bhutanese counterpart Jigme Y Thinley and Indian's Ambassador to Bhutan Pavan Varma at Paro International airport, 60 km from the capital.
Singh was offered a warm reception and a guard of honour.
He is expected to meet Pakistan Prime Minister Yousuf Raza Gilani during the two-day summit of eight member countries, which will be inaugurated later in the day.
Singh will hold discussion with the leaders from other member countries.
"The winds of change are blowing across the world. South Asia cannot be immune to the trend of greater integration, both at the regional and global levels," the prime minister had said last night, on the eve of his departure.
Singh said that the summit will help the leaders of the member countries to collectively introspect on "where we are, what more we can do together to meet the developmental aspirations of our people, and how South Asia can play its rightful role in the international arena."
"I also look forward to my meetings with leaders of other Saarc countries," the prime minister said, without elaborating.
A detailed discussion on the issue of climate change, which is the key theme of the summit, will be held between the leaders and the Saarc leaders will come out with a Special Saarc Declaration on Climate Change.
During the summit, leaders from Afghanistan, Pakistan, SriLanka, the Maldives, Bangladesh, Nepal, Bhutan and India will sign two Saarc agreements on Environment and Trade in Service.