Shares in Samsung fell by 7.5% in Seoul on Monday after a ruling by a federal court in the United States in favour of Apple.
The BBC reports it was the largest one-day drop in the cmpany's share price for nearly four years.
On Friday, a jury in San Jose, California, ruled that Samsung had infringed Apple patents for mobile devices. A fine of $US1.05 billion was imposed.
Samsung said it would appeal against the verdict.
A court in South Korea also ruled on Friday ruled that both Apple and Samsung had copied each other.
Samsung is the world's biggest technology company.