The US singer also confirmed they are called Sir Carter and Rumi - which had been rumoured after she and husband Jay-Z filed a trademark for the names.
The picture showed the 35-year-old mother-of-three and the twins draped in a purple floral sheet, while she wore a blue veil.
Jay Z and Beyonce
It clocked up more than a million likes on Instagram in less than an hour.
The style of the image, in which Beyonce stands in a garden barefoot in front of a floral archway, echoes the photoshoot she used to announce her pregnancy.
As well as the twins, a girl and a boy, she and rapper Jay-Z are also parents to five-year-old daughter, Blue Ivy.