During the ceremony, Rajoelina repeated his pledges to hold presidential and parliamentary polls within two years and to draft a new constitution.
"Today we proclaim the end of dictatorship, of waste in the management of the state's affairs, the end of the lies, empty promises ... that have for too long stifled Madagascar's political life," he said.
"Before the Madagascan people and before God, I swear that I will do my utmost for the good of the people and I swear that I will respect Madagascar's laws."
But Stephen Ellis, an expert on Madagascar from the Free University of Amsterdam, told Al Jazeera Rajoelina may face some hurdles in winning the support of the country as a whole.
"In the view of international comdemnation, I don't think [Rajoelina] will be able to hold out for two years ... he needs to regularise his position sooner than that but it will be difficult," he said.
"[His claim to power] is clearly unconstitutional and there is going to be a period of instability."
Diplomatic boycott
The US has cut off non-humanitarian aid to Madagascar due to Rajoelina's "coup", while the African Union (AU) has suspended its membership calling the change of power "unconstitutional".
The Southern African Development Community (Sadc), a regional bloc, has also refused to recognise Rajoelina's leadership, and member states are reportedly discussing imposing sanctions against the island.
Bruno Nongoma Zidouemba, the chairman of the AU's peace and security council, said that "what occurred in Madagascar enters the definition of unconstitutional change of government".
"The council then decided to suspend the participation of Madagascar to the bodies and organs of the AU," he said.
Rajoelina, who at 34-years-old is still six years too young to hold the presidency under the current constitution, tried to address some of the international concerns on Saturday.
"To all the peoples and rulers of friendly and partner countries, to donors ... who are watching today: be assured that Madagascar is a friend to every nation and citizen in the world," he said.
"You must know that we want change in the way our country is governed and are determined to implement the rules and principles of good governance."
Legal approval
After losing control of the government and the army, Ravalomanana, 59, conceded power to a military directorate, which in turn passed it to Rajoelina.
Madagascar's constitutional court on Wednesday ruled that the double transfer was legal and that Rajoelina was the country's rightful interim leader.
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| The AU has suspended Madagascar, calling the takeover 'unconstitutional' [Reuters] |
At least 2,000 of Ravalomanana's supporters held a counter-rally on Saturday at Antananarivo's Democracy Square.
Ravalomanana's whereabouts are still unknown.
"I'm sure Ravalomanana still has quite a lot of support in the country," Ellis told Al Jazeera.
"He's always been close to the Protestant church which is a very important opinion former in the country ... I don't think his supporters are just going to fade away or lie down and take this."
Rajoelina, who spent months calling for Ravalomanana to step down, has promised to bring food prices down on the Indian Ocean island, where three-quarters of the population live on less than $2 a day.
He also said he would sell a jet that Ravalomanana recently bought for $60m, and use the money "to establish a hospital for the people's health, which is a higher priority".
Rajoelina has also cancelled an agreement to lease South Korean corporation Daewoo more than a million hectares of land to grow food crops.
Ravalomanana was heavily criticised for the deal.
Rajoelina has said Ravalomanana should be prosecuted for alleged crimes, including the use of lethal force against unarmed opposition demonstrators in recent weeks.
His government has banned Ravalomanana's ministers from leaving the country.