National Trust members are to vote on whether to ban GM crops on National Trust land at its November AGM, as a result of a members' resolution.
But the vote is not binding on the Trust, and the charity has said it wants a better understanding of the impact of the crops before making a decision on whether it will grow them commercially.
The statement follows the results of trials which found that some types of GM crops harm wildlife while others were kinder than normal crops.
The Trust's position echoes that of the Government but contrasts with that of environmental groups such as Friends of the Earth and Greenpeace that want an immediate ban.
The Trust owns 250,00 hectares of land, 80 per cent of which is farmed by 700 tenant farmers.
Director of policy and strategy Tony Burton said: "A decision can only be made after thorough testing and a thorough understanding of the state of public opinion."