THE Housing Executive owns more than 500 acres of unused or underdeveloped land across the north.
A total of 71 acres of land owned by the body has been "declared surplus for disposal".
A further 479 acres of undeveloped land is also owned by the housing organisation.
The figures were revealed in answer to an assembly question to Social Development minister Mervyn Storey to "outline the current area in hectares of both surplus and undeveloped land owned by the Northern Ireland Housing Executive".
He said there was a "total of 223 hectares (551 acres) of undeveloped land on their undeveloped land schedule".
But SDLP assembly member Dolores Kelly, who sits on the Social Development committee, said she was concerned by the figures.
"It is hugely important that something is done with this land, be it used or sold to bring money into the coffers," she said.
"It is of huge concern that some land is being left idle, especially when some of it could be commercially useful.
"We would like to see a more proactive approach to dealing with this land and I would urge the minister to have a look at this.
"In my own constituency of Upper Bann, I am working proactively with the Housing Executive to try and encourage new builds but unfortunately that is not always possible."
A Housing Executive spokesman said it "has an active programme of land use".
"Our priority is to use any vacant sites in our ownership for social housing where possible, however, if there is no development potential, we will dispose of the site to reach maximum value in compliance with public sector asset management requirements," he said
"Over the past two years we have transferred 36 sites (21.22 hectares) to housing associations, providing over 450 new social homes for people on the waiting list.
"A further 29 hectares have been identified for transfer to housing associations to facilitate the three-year Social Housing Development Programme.
"Also, 29 hectares have been declared as surplus to requirement. We regularly review each of these sites to ensure the earliest disposal of surplus land can be achieved, at the best value obtainable.
"We are currently examining the remaining 165 hectares for their development potential for social housing or other suitability and are carrying out a programme of economic appraisals on each of these sites."
