Under the offer, GrainCorp is offering one GrainCorp share for every nine Ridley shares.

"This is an unsolicited, conditional takeover offer by GrainCorp and we urge shareholders to take no action until the offer is reviewed in detail by the board," Ridley chairman, Dr John Keniry, said.

"Ridley has articulated a decisive strategy to deliver significant returns to shareholders.

"These initiatives include the sale of Ridley Inc, the realisation of surplus land holdings (which have been independently valued in excess of $A80million), and addressing underperforming business units within the AgriProducts division. Ridley will continue to pursue those initiatives.

"The company also has new leadership at both board and management level following changes to the board and the appointment last week of John Murray as the company's new MD and CEO."

Ridley has retained Gresham Advisory Partners as financial advisor and Allens Arthur Robinson as legal advisor.

The board will make a further announcement in response to the takeover offer next week.

Ridley shares are this morning trading at $1.43, up from Friday's close of $1.40.