China's social security fund last year had the worst investment return since 2008 due to the weak domestic stock market.

The National Social Security Fund, which manages the country's social security fund worth 869 billion yuan (US$136 billion), earned 7.4 billion yuan last year, according to the fund's annual financial report published in the China Securities Journal yesterday.

The return on investment was 0.84 percent last year, compared with 4.2 percent in 2010 and the average of 8.4 percent since the fund's establishment in 2000.

"Lasting weakness of the stock market has hurt the investment return, but returns on fixed income products and industrial assets have contributed a lot to the fund," the report said.

By the end of 2011, 50.7 percent of the fund's assets were invested in fixed income products, 32.4 percent in stocks, and 16.3 percent in state-owned companies in the form of private equity investments, the report said.

The fund's interest income increased 4.6 billion yuan to 19 billion yuan and the earnings from equity investment nearly tripled to 107 million yuan from 35 million yuan, while the value of tradable assets shrank by 35.8 billion yuan, the report said.

Starting in 2003, the fund has been allowed to invest at most 40 percent in the stock market. By the end of 2011, an average 20 percent of the fund's capital each year was invested in stocks.