Aviva is selling 15% of its stake in Delta Lloyd and will no longer be the majority shareholder in the Dutch insurer.
The placing of approximately 25 million Delta Lloyd shares are priced at €17.25 per share, Aviva says.
Aviva shares fell 1.66% to 445.2p at 10.30am, after this morning's offering.
Aviva expects gross cash proceeds of £381m from the sale.
The insurer's disposal of 15% of Delta Lloyd's issued ordinary share capital will cut its holding from a controlling stake of 58% to one of 43%.
Aviva says the move is consistent with its strategy of focusing on twelve markets where it has strength and scale, which will no longer include the Benelux region.
Cash proceeds from the sale will boost Aviva's liquidity and further strengthen its balance sheet.
The offer price will be determined after an accelerated book-building process which starts today.
Aviva shareholders must approve the sale at an extraordinary general meeting expected on 4 May 2011.
Andrew Moss, group chief executive of Aviva, says: "Reducing our shareholding in Delta Lloyd is consistent with our focus on pursuing profitable growth in markets where we have strength and scale."
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