This paper examines the U-shaped iron blade discovered from Yangdong-ri Tomb No. 5 in Bongsan county. This region belonged to the Nangnang Commandery in ancient time. Accordingly, this paper compares this artifact with other U-shaped iron blades discovered in the Nangnang region and contextualizes this type of artifact with the iron agricultural tools of Nangnang in general. U-shaped iron blades were used to plow agricultural fields in Nangnang. Iron agricultural tools were presumably used in the northwestern region of the Korean peninsula during the Gojoseon period. However, direct evidence of iron tools only appears for the subsequent period with the establishment of the Nangnang Commandery. In the Nangnang region, U-shaped iron blades similar to those of the Chinese Han state were used in the beginning. After the third century CE, blades changed stylistically and those similar to the Yangdong-ri Ushaped iron blade became prevalent. Eventually, U-shaped iron blades of typical Goguryeo style emerged. U-shaped iron blades of Nangnang are discovered from tombs and settlements. These tombs are either log tombs or brick-chamber tombs, and settlements are mostly earthen fortresses. In contrast with the U-shaped iron blades of Goguryeo, Baekje and Silla, those of Nangnang are found from both tombs and settlements in equal proportions. Earthen fortresses, which are classified as settlements in this paper, presumably functioned as the administrative offices of the state. These sites were either the administrative offices of the Nangnang Commandery or the administrative offices of the prefectures that belonged to the commandery. Log tombs and brick-chamber tombs are also considered to be the tombs of the ruling class. Most importantly, the U-shaped iron blade of Yangdong-ri Tomb No. 5 is stylistically different from those of the Chinese Han state. Rather, this artifact shows stylistic transition from the U-shaped iron blades of the Han state to those of Goguryeo.