Cao will be the first Vietnamese-American in Congress.
Republicans made an aggressive push to take the seat from the 61-year-old incumbent, who has pleaded not guilty to charges of bribery, laundering money and misusing his congressional office.
The election was one of two in Louisiana postponed because of Hurricane Gustav.
During an FBI sting two years ago, $90,000 in marked currency was found in a freezer in congressman Jefferson’s home as reported here.
William Jefferson’s re-election loss is reported here.