Seventeen Latin American governments, the United States and Canada rejected the legitimacy of Mr Maduro’s next term in a measure adopted on Thursday.
Most countries from Europe and Latin American did not send representatives to the swearing-in.
But Cuba’s President Miguel Diaz-Canel, Bolivian President Evo Morales and President Anatoli Bibilov of a breakaway province of Georgia were among the few foreign leaders who attended the ceremony at the country’s Supreme Court.
Venezuela is the centre of a world war led by the North American imperialists and its allies
In a speech after his swearing-in, Mr Maduro claimed 94 countries had sent representatives to his inauguration.
He vowed to continue the legacy of the late president Hugo Chavez and accused the United States of trying to ignite unrest through its increasing economic sanctions.
“Venezuela is the centre of a world war led by the North American imperialists and its allies,” said Mr Maduro, a former bus driver.
“They have tried to convert a normal inauguration into a world war.”
Mr Maduro’s second term extends Venezuela’s socialist revolution amid widespread complaints that he has stripped the country of its last vestiges of democracy.
Mr Maduro, 56, denies that he is a dictator and often blames President Donald Trump for leading an economic war against Venezuela that is destroying the country.
The Organisation of American States voted not to recognise Mr Maduro’s legitimacy, adopting a resolution presented by Colombia, Argentina, Brazil, Chile, Costa Rica, the United States, Paraguay and Peru.
The move was denounced by Venezuela’s ambassador to the OAS, Samuel Moncada, as “a hostile act … against the will of our nation”.
Paraguay went a step further, cutting diplomatic ties.
President Mario Abdo Benitez said his country “in the exercise of its constitutional powers and national sovereignty, adopts the decision to break diplomatic relations with the Bolivarian Republic of Venezuela”.
US secretary of state Mike Pompeo said in a statement that the United States will keep up pressure in support of the Venezuelan people.
“It is time for Venezuelan leaders to make a choice,” Mr Pompeo said, urging Maduro supporters to be on the right side of history.
“Now is the time to convince the Maduro dictatorship that the moment has arrived for democracy to return to Venezuela.”
Nicolas Maduro today is making a mockery of democracy
Argentina’s President Mauricio Macri also denounced Mr Maduro, saying he lacks the authenticity won through honest elections despite Thursday’s elaborate inauguration ceremony and any other “tricks”.
“Nicolas Maduro today is making a mockery of democracy”, Mr Macri said on Twitter.
“Venezuelans know it, the world knows it. Venezuela lives under a dictatorship.”
Oil-rich Venezuela was once among Latin America’s wealthiest nations.
It produced 3.5 million barrels of crude daily when Mr Chavez took power.
Output now has plummeted to less than a third of that.
Critics blame years of rampant corruption and mismanagement of the state-run oil firm PDVSA.