A bronze dagger excavated from the historical site at Bongili in Gyeongju was examined for its microstructure and chemical compositions. The results show that it was forged out of the Cu-10 weight % Sn alloy having no lead. The application of forging in fabrication and the use of an unleaded alloy distinguish this artifact from other bronze daggers that have been reported in Korea, the majority of which were cast from leaded Cu-Sn alloys. This dagger is a rare and valuable archaeological material suggesting a unique bronze technology practiced in ancient Gyeongju area.