STX Corp fell its daily maximum of 15 percent to 62,600 won. Shares in STX Shipbuilding also dropped 13.04 percent to 29,350 won and STX Engine lost 14.27 percent to 42,050 won.
"STX is not exactly in the best financial shape, and the fact that it keeps raising additional capital is unsettling investors," said Yoon Pil-joong, an analyst at Samsung Securities.
Shares in STX Pan Ocean were also down 6.24 percent to 1,955 won.