The deal is part of Zoopla's strategy to expand its reach and be "the most comprehensive property website". Visitors to Upmystreet.com will now automatically be redirected to Zoopla.co.uk with immediate effect.
Upmystreet.com attracted 1.1 million unique visitors in March 2012, which is an 18.2% increase year on year, according to comScore data.
It attracts a third of the traffic Zoopla.co.uk does, which saw 3.2 million unique UK visitors in March, up 7.9% from last year, according to comScore.
It has not confirmed further plans for the site and whether it will maintain the brand.
Alex Chesterman, founder and chief executive of Zoopla, said: "This acquisition is a natural fit for us and allows us to further extend our audience and reach for the benefit of our members."
The announcement comes after Zoopla was given the green light by the Office of Fair Trading to merge with DMGT's Digital Property Group, which owns FindaProperty.com and Primelocation.com, in a bid to take on Rightmove. The deal is expected to close in the next few weeks.
Rightmove.com is the most visited property site by UK internet users, receiving 6.9 million unique visitors in March 2012. It is followed by Digital Property Group's two sites, which received 3.8 million uniques for the same period, according to comScore.