Oxfam says there's been an increase in international companies buying land in poor parts of the world, displacing farmers and leaving poor communities homeless.
In a report, the British charity says more than 200 million hectares of land has been sold or leased worldwide since 2001.
It says half the deals have been in Africa, where 35 million hectares, a total area as large as Germany, has been bought.
The report focuses on Uganda, South Sudan, Honduras, Guatemala and Indonesia.
Oxfam chief executive Barbara Stocking said land grabs had accelerated especially since 2008, when soaring prices highlighted the issue of food security.
''Investors, no matter how noble they pertain to be, cannot sweep aside the needs and rights of poor communities who depend on the land they profit from,'' she said.
The report said an increasing demand for food, combined with climate change and the increase of agricultural land being used to grow biofuels, meant that the number of such deals would be likely to only rise in the future.