The 1991 KAL Cup Korea Open was a men's tennis tournament played on outdoor hard courts that was part of the World Series of the 1991 ATP Tour.

It was the fifth edition of the Seoul Open and was played at Seoul in South Korea from 15 April through 22 April 1991.

Unseeded Patrick Baur won the singles title.

[3] Patrick Baur defeated Jeff Tarango 6–4, 1–6, 7–6(7–5) Alex Antonitsch / Gilad Bloom defeated Kent Kinnear / Sven Salumaa 7–6, 6–1