The National Council for Social Security Fund (SSF) has promised to invest 10 billion yuan (1.5 billion U.S. dollars) in the China Development Bank (CDB), one of the country's three policy lenders, the bank announced Wednesday.

Under a contract signed by both sides, as well as by the Ministry of Finance and Central Huijin Investment Ltd., the investment will allow the SSF to hold a 2.19 percent stake in the CDB as a strategic investor.

The SSF's investment is part of the bank's reform program and will help boost its capital, said the CDB in a press release, adding that the move will enhance capital sources and investment programs for both sides.

Buying CDB shares is another significant investment by the SSF following its stake purchase of the Bank of China, the Bank of Communications, the Industrial and Commercial Bank of China and the Agricultural Bank of China.

The move is not only beneficial to the CDB, but will also help preserve and increase the SSF's value, said the CDB statement, citing an official from the SSF.