Rosie and Ruby Formosa were born joined at the abdomen and sharing part of the intestine.
The twins, now 12 weeks old, were operated on at London's Great Ormond Street Hospital the day after they were born on 27 July.
Their mother Angela, from Bexleyheath in south-east London, said the "smiling bubbly babies" were doing well.
The twins needed an emergency operation to separate them.
Mrs Formosa, 32, said finding out the twins were joined had been a shock after her "textbook" pregnancy with first daughter Lily, now aged five.
The twins are now putting on weight and starting to smile, their mother said
"At an early pregnancy scan they said the twins looked very close together so I went to King's College for another scan," she said.
"Between 16 and 20 weeks we found out that they were joined - I didn't know what to think, I was shocked and I felt sad.
"We didn't know what to expect until they were born - the doctors could not tell where they were connected.
