Colchester sisters Rebecca and Rachel Croly took part in the Kent Open in Mepoham, Kent.
They competed in separate kumite (fighting) sections and battled their way through three rounds each.
Rebecca, 13, came away with gold and Rachel, 11, with silver.
In Rebecca's fighting section (13 to 16 years), there were some anxious moments with some competitors at the upper end of her age group weighing 40kg more.
However, the girls' sharp punches, kick combinations, speed and agility gave them the edge to win through.
The sisters, from the Gilberd School, Highwoods, train in Korean karate at SD School of Martial Arts.
Sean Doyland, chief instructor there, said: "I'm pleased the girls won.
"They are both members of the elite squad and are winning in kumite sections at competitions across the country.
"The whole school has been very successful in competition this year in both kata and kumite."
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