The opposition has called for mass protests to defend the parliament building and there are concerns that further violence could break out in the crisis-hit country. At least 123 people have died in anti-government protests since April.
Maduro's announcement came despite accusations from the company which runs the country's voting systems that turnout figures were inflated by authorities in Sunday's vote to choose the 545 new delegates.
The election drew worldwide condemnation, with the Unites States imposing sanctions on Maduro. The European Union said it would not recognize the Constituent Assembly.
The body's creation was also opposed by the Democratic Unity Roundtable (MUD), a coalition of more than 30 Venezuelan opposition parties, which sees it as a bid to usurp the authority of the National Assembly, where it won a two-thirds majority in 2015.