Hugo Chavez shocked Venezuelans when he called the constitution "moribund" during his presidential oath last February.
On Wednesday, the former coup leader took the oath again _ this time in front of an assembly controlled by his leftist coalition and empowered to scrap the old constitution and write a new one.
Right hand raised, the president said he wouldn't rest until Venezuela has "buried" the past.
"If 200 days ago I swore over a moribund constitution, today I am swearing before a midwife who will bring about the historic birth of a new Venezuela," Chavez said.
Wednesday's swearing-in took place two days after the constitutional assembly, whose 131 delegates were elected July 25, ratified Chavez as president. He had officially placed his job at the assembly's disposal, a largely symbolic move since his supporters control 92 percent of the seats.
The assembly, Chavez's main policy initiative, has six months to write a new constitution. Chavez wants the body to do away with government institutions he says are plagued with corruption and responsible for squandering the country's vast oil wealth.
The president has asked the opposition-controlled Congress and Supreme Court to put themselves at the assembly's mercy.
But Chavez said there was "no need" to dissolve them until after a constitutional referendum.