The banks' way of doing business appears to have changed little, with loans made failing to reflect their corporate borrowers' level of risk, the IMF said in a working paper published Thursday.

"Important concerns about governance and internal controls remain," the IMF document said, citing high-level corruption cases at the China Construction Bank and Bank of China as examples.

"While the formal corporate governance structure has changed substantially, the way business is done may not have changed much just yet," it said.

The other two big state banks are the Industrial and Commercial Bank of China (ICBC) and Agricultural Bank of China.

The lending institutions, which China has been preparing for oncoming foreign competition, were supposed to clear their bad loans and move towards more rational lending.

However, there is little indication the banks have shed their decades-long bad habit of lending to mostly state-owned companies that are often unprofitable, according to the report's findings.

"In the 1997 to 2004 data, it is difficult to find solid empirical evidence of a strong shift to commercial orientation by state-owned commercial banks," the IMF said.