It was kidnapped on its way to a slaughter house by a group of artists who won't reveal their names.
The cow was lifted by crane on to the top of the building in the Chilean capital, reports Las Ultimas Noticias.
It will live on the 1,500sq ft rooftop, which has been remodelled as a farm, for a week.
The cow will be cared for and milked daily during the week and afterwards the artists plan to release it on a nature reserve.
A spokesperson for the group said: "We want to question the limits of the art creation. People think art is only what is in the galleries but that is not true."