After taking the oath of office before bewigged Chief Justice Godfrey Chidyausiku at a sun-drenched soccer stadium in Harare, Mugabe praised African countries that endorsed the July 31 vote and told his critics to "go hang."
"Except for a few Western dishonest countries, our elections have been hailed as peaceful, free, fair and credible," he said in an hour-long speech to thousands of cheering supporters, diplomats and six African presidents.
"For those odd Western countries who happen to hold a different negative view of our electoral process and outcome, there is not much that we can do about them. We dismiss them as the vile ones whose moral turpitude we must mourn," he added.
As he was sworn in, former colonial power Britain and the European Union repeated serious reservations about the credibility of the vote, already rejected by Mugabe's main rival, Morgan Tsvangirai, as a fraudulent "coup by ballot."
The new term will be Mugabe's fifth as president and extends his 33-year rule. He also served as prime minister after the end, in 1980, of white minority rule in the country previously known as Rhodesia.
That power-sharing deal with Tsvangirai's MDC party brought stability to an economy crushed by hyperinflation. Analysts are worried that with Mugabe's ZANU-PF now back in full control, the government may roll back reforms that had helped spur some growth.
Mugabe said his ZANU-PF party would advance an "indigenization" policy that forces foreign mining firms in the country to turn over majority stakes to local blacks, making it the centerpiece of its post-election economic revival program.
"The time has now come for us to extend our dominion to all those resources which the Almighty has been generous enough to give. That is the next revolution whose first step is this administration, this new government," he said.
His opponent in the last three elections, Tsvangirai, who has branded the election a "huge fraud," boycotted the ceremony.
A Movement for Democratic Change (MDC) spokesman said the party did not want to be associated with "election thieves." ZANU-PF has rejected all allegations of vote-rigging.
In his speech, Mugabe praised Tsvangirai for helping ensure a peaceful vote and being a partner in the coalition that produced a new constitution in March.
Britain said on Thursday Mugabe's re-election could not be deemed credible without an independent investigation into allegations of voting irregularities.
U.S. officials this week said the election was flawed and Washington had no plans to loosen sanctions until there were signs of change in the country.
Mugabe and senior ZANU-PF officials are the target of sanctions imposed by governments in the West, who accuse them of a history of human rights violations and vote rigging.
The European Union will review relations with Zimbabwe because of its "serious concerns" about the election, EU foreign policy chief Catherine Ashton said on Thursday. Its verdict on the fairness of the vote will be crucial to a decision on whether it continues to ease sanctions.
The stadium was filled with cheering, dancing supporters wearing ZANU-PF colors.
"It's Africa versus Europe, with Zimbabwe as the new battlefront," read one banner, reflecting the support former guerrilla chief Mugabe can still muster as a liberation war hero.
Unlike African monitors, Western observers were barred from travelling to Zimbabwe to scrutinize the July 31 vote.
After the voting went ahead peacefully, domestic monitors from the Zimbabwe Election Support Network said registration flaws might have disenfranchised up to a million people.
But observer missions from the regional 15-nation Southern African Development Community (SADC) and the African Union broadly endorsed the vote as free and peaceful and called on all parties to accept its results.
Mugabe, once dubbed the "thinking man's guerrilla" because of his bookish demeanor and the academic degrees he earned in jail in Rhodesia, used his speech to fire fresh barbs at his "neo-colonialist" foes.
He accused Britain, the United States, Canada and Australia of seeking to impose their political will on his state.
"Having struggled for our independence, our fate has irrevocably orbited out of colonial relations, indeed can no longer subsist in curtseying and bowing to any foreign government, however powerful it feigns itself to be and whatever filthy lucre it flaunts," he said to cheers.