Vietcombank sold the dollar at VND24,495, down 0.20% from Tuesday.
The State Bank of Vietnam raised its reference rate by 0.08% to VND24,079.
The greenback was sold at VND24,430 on the black market, up 0.33%.
It has increased by 3.22% against the dong since the beginning of the year.
Globally the dollar remained firm on Wednesday but softened slightly against the yen ahead of a much-anticipated rate decision by the Federal Reserve later in the day, Reuters reported.
The U.S. dollar index, which measures the greenback against a basket of rivals, stayed mostly flat at 105.13 as traders awaited the Fed’s rate decision.
Markets expect the Fed will almost certainly keep rates on hold at 5.25% to 5.50%, putting the focus on the central bank’s forward guidance.