The figure represents an increase of $1.6 billion from $369.9 billion a month earlier, according to the Bank of Korea (BOK).
BOK officials attributed the increase to a rise in returns on foreign currency asset management.
As of the end of April, South Korea remained at No. 6 in the world in terms of FX reserves, the BOK said.
China continued to top the list with $3,730 billion (as of the end of March), followed by Japan ($1,250.1 billion), Saudi Arabia ($686.4 billion), Switzerland ($599.6 billion) and Taiwan ($418.2 billion).
Brazil came in seventh with $364.5 billion, Russia eighth with $356.0 billion, India ninth with $351.9 billion and Hong Kong 10th with $343.2 billion.