The ceremony was led by National Assembly Speaker Diosdado Cabello in the capital, Caracas.
Mr Chavez, who died on 5 March after a long battle with cancer, had named Mr Maduro as his chosen successor.
The country's 1999 constitution says the National Assembly speaker becomes interim president in the event of a president-elect's death or inability to be sworn in. The constitution also says a presidential election should be called within 30 days.
However, the main opposition coalition boycotted Mr Maduro's swearing-in, saying that it was unconstitutional.
It argues that - under the constitution - the speaker of the National Assembly should be the one to take over as acting president.
The opposition leader, Henrique Capriles, called the move fraudulent.
Follow us on Telegram
t.me/apanewsaz
Follow us on Instagram
Follow us on TikTok
Follow us on Facebook
Follow us on X
