On Thursday, the bank said it would buy up to $100 million, accepting bids at an exchange rate between 24.8150-24.8300 hryvnias per dollar.
Banks offered $81.4 million. At its last auction on June 22, the central bank bought $22.4 million at 24.89-24.90 per dollar.
Meanwhile, the hryvnia's average rate on the interbank market firmed to 24.8242 from 24.8544 per dollar in the previous day.
The central bank has bought $429.6 million since early June, following its requirement to banks to sell part of their foreign exchange earnings.