Ajoke Bello, 32, gave birth to the six babies by Caesarean section operation on Thursday and was initially in a stable condition.
But she developed complications from excessive bleeding at hospital in Sagamu, Ogun State, south-west Nigeria.
The naturally conceived babies - three girls and three boys - were in a stable condition, said medical officials.
Two of the babies were transferred on Saturday to the intensive care unit of a private hospital in Lagos, where their condition improved. But Mrs Bello died at the Olabisi Onabanjo University Teaching Hospital in the early hours of Sunday.
According to the figures from the World Health Organization, published in 2007, Nigeria's maternal mortality rate is the second highest in the world, after India.
