IDB said in a statement on Wednesday it sold the stake in an off-market transaction at a price of NIS 13.3 per share, below its closing price of NIS 15 on Tuesday in Tel Aviv.
IDB Development will post a gain of NIS 22 million ($5.9 million) from the sale.
The deal follows IDB's sale of 49.9% of CII to US-based Access Industries for NIS 1.27 billion ($340 million) last July.
CII, with a market value of NIS 2.4 billion ($640 million), is one of Israel's leading investment companies with holdings ranging from manufacturing-oriented activities to technology companies. It also operates units to manage its investments in biotechnology and other venture capital investments.
IDB Development is a holding company and subsidiary of IDB Holding, which has said it would take steps to increase its liquidity significantly to pay off a high debt load.