Hyundai's Accent and Kia's Rio, called Pride in South Korea, sold 8,208 and 2,802 units, respectively for a combined total of 11,010, compared with 9,646 vehicles for Nissan, according to Autodata.
The figure for Hyundai-Kia represents a 14.3 percent increase from the same month of last year.
Hyundai-Kia took up a 25 percent share of the market in April, up from 23 percent in March, 21 percent in February and 19 percent in January.