Munich Re said it has sold four million shares in German insurer Allianz AG Holdings for €375m (£257m).
Deutsche Bank handled the placement.
The four million shares represented a stake of about 1% in Allianz's share capital.
According to reports, Munich Re had held 8.98%, or 34.6 million shares, in Allianz at the end of December 2004.
The stock was placed at €94 per share, dealers said.