Vietcombank sold the dollar at VND24,140, up 0.29% from Tuesday. This is the highest level the bank has sold the greenback this year.
The State Bank of Vietnam kept its reference rate stable at VND23,898.
The dollar was at VND24,060 on the black market, down 0.33%. It has gained over the dong by 1.73% since January 1.
Globally the U.S. dollar perched near a two-month peak on Wednesday as investors looked to the Federal Reserve chair's speech this week for cues on the path of monetary policy, while the yen loitered near 146 a dollar, keeping traders guessing on any intervention, Reuters reported.
The dollar index, which measures the U.S. currency against six rivals, was at 103.55, not far from the two-month high of 103.71 it touched on Tuesday. The index is up 1.6% in August and is on course to snap its two-month losing streak.
A recent run of strong U.S. economic data has helped allay worries of an impending recession but with inflation still well above the Fed's target of 2%, investors are wary that the central bank may keep interest rates in a higher range for longer.