Treasurer Scott Morrison has again knocked back the sale of Australia's largest private land holding to Chinese conglomerate Shanghai Pengxin Group, concluding it was not in the national interest.

The S. Kidman & Co portfolio constitutes the country's largest private land holding, accounting for 1.3 per cent of total Australian land and 2.5 per cent of all agricultural land.

Mr Morrison said he remained concerned that the size and significance of the sprawling Kidman portfolio being sold as a single entity put it out of the reach of a domestic buyer.

"The size of the asset makes it difficult for any single Australian group to acquire the entire operation," he said. He stressed the decision reflected only his "preliminary view" and the relevant parties would be able to respond to his findings by Tuesday.