In the first quarter, the BOK sold a net $103 million to stabilize the Korean currency's movement, compared with a net purchase of $11.5 billion three months earlier.
The central bank began releasing such data in March 2019 to help boost the transparency of its market stabilization steps.
A BOK official said market smoothing operations in the second quarter came as the won's movement stabilized.
The Korean currency closed at 1,128.5 won against the US dollar on June 30, compared with 1,131.8 won at the end of March. (Yonhap)